Glucosyltransferase amino acid motifs for enzymatic production of linear poly alpha-1,3-glucan

ABSTRACT

Reactions comprising water, sucrose, and one or more glucosyltransferase enzymes are disclosed herein. Glucosyltransferase enzymes used in these reactions comprise certain motifs allowing production of insoluble poly alpha-1,3-glucan having at least 95% alpha-1,3 glycosidic linkages.

This application is a continuation of U.S. application Ser. No. 15/182,747 (filed Jun. 15, 2016), which claims the benefit of U.S. Provisional Application Nos. 62/180,779 (filed Jun. 17, 2015) and 62/180,788 (filed Jun. 17, 2015), all of which prior applications are incorporated herein by reference in their entirety.

REFERENCE TO SEQUENCE LISTING SUBMITTED ELECTRONICALLY

The official copy of the sequence listing is submitted electronically via EFS-Web as an ASCII formatted sequence listing with a file named 20181113_CL6452USCNT_SequenceListing.txt created on Nov. 13, 2018, and having a size of 704 kilobytes and is filed concurrently with the specification. The sequence listing contained in this ASCII-formatted document is part of the specification and is herein incorporated by reference in its entirety.

FIELD OF INVENTION

The present disclosure is in the field of enzyme catalysis. For example, the disclosure pertains to producing linear poly alpha-1,3-glucan using a glucosyltransferase having certain amino acid sequence motifs.

BACKGROUND

Driven by a desire to find new structural polysaccharides using enzymatic syntheses or genetic engineering of microorganisms or plant hosts, researchers have discovered polysaccharides that are biodegradable and can be made economically from renewably sourced feedstocks. One such polysaccharide is poly alpha-1,3-glucan, a glucan polymer characterized by having alpha-1,3-glycosidic linkages. This polymer has been isolated by contacting an aqueous solution of sucrose with a glucosyltransferase (GTF) enzyme isolated from Streptococcus salivarius (Simpson et al., Microbiology 141:1451-1460, 1995).

U.S. Pat. No. 7,000,000 disclosed the preparation of a polysaccharide fiber using an S. salivarius gtfJ enzyme. At least 50% of the hexose units within the polymer of this fiber were linked via alpha-1,3-glycosidic linkages. S. salivarius gtfJ enzyme utilizes sucrose as a substrate in a polymerization reaction producing poly alpha-1,3-glucan and fructose as end-products (Simpson et al., 1995). The disclosed polymer formed a liquid crystalline solution when it was dissolved above a critical concentration in a solvent or in a mixture comprising a solvent. Continuous, strong, cotton-like fibers were obtained from this solution that could be spun and used in textile applications.

Not all glucosyltransferase enzymes can produce glucan with a molecular weight and percentage of alpha-1,3 glycosidic linkages suitable for use in spinning fibers. For example, most glucosyltransferase enzymes do not produce glucan having at least 50% alpha-1,3 glycosidic linkages and a number average degree of polymerization of at least 100. Therefore, it is desirable to identify glucosyltransferase enzymes that can convert sucrose to glucan polymers having a high percentage of alpha-1,3 glycosidic linkages and high molecular weight.

Reactions are disclosed herein that comprise glucosyltransferase enzymes containing certain amino acid motifs. These enzymes can synthesize high molecular weight, linear alpha-1,3-glucan polymer. Also disclosed are methods for identifying such enzymes.

SUMMARY OF INVENTION

In one embodiment, the disclosure concerns a reaction solution comprising water, sucrose, and a glucosyltransferase enzyme, wherein the glucosyltransferase enzyme comprises a catalytic domain comprising the following three motifs:

-   -   (i) a motif comprising an amino acid sequence that is at least         90% identical to SEQ ID NO:78,     -   (ii) a motif comprising an amino acid sequence that is at least         90% identical to SEQ ID NO:79, and     -   (iii) a motif comprising an amino acid sequence that is at least         90% identical to SEQ ID NO:80;         wherein the glucosyltransferase enzyme does not comprise         residues 54-957 of SEQ ID NO:65, residues 55-960 of SEQ ID         NO:30, residues 55-960 of SEQ ID NO:4, residues 55-960 of SEQ ID         NO:28, or residues 55-960 of SEQ ID NO:20; and wherein the         glucosyltransferase enzyme produces insoluble poly         alpha-1,3-glucan having at least 95% alpha-1,3 glycosidic         linkages and a weight average degree of polymerization (DP_(w))         of at least 100.

In another embodiment, the catalytic domain comprises an amino acid sequence that is at least 90% identical to amino acid positions 54-957 of SEQ ID NO:65.

In another embodiment, the position of the amino acid sequence that is at least 90% identical to SEQ ID NO:78 aligns with amino acid positions 231-243 of SEQ ID NO:65; the position of the amino acid sequence that is at least 90% identical to SEQ ID NO:79 aligns with amino acid positions 396-425 of SEQ ID NO:65; and/or the position of the amino acid sequence that is at least 90% identical to SEQ ID NO:80 aligns with amino acid positions 549-567 of SEQ ID NO:65.

In another embodiment, motif (i) comprises SEQ ID NO:78, motif (ii) comprises SEQ ID NO:79, and motif (iii) comprises SEQ ID NO:80.

In another embodiment, the glucosyltransferase enzyme synthesizes poly alpha-1,3-glucan having 100% alpha-1,3 glycosidic linkages.

In another embodiment, the glucosyltransferase enzyme synthesizes poly alpha-1,3-glucan having a DP_(w) of at least 400.

Another embodiment of the disclosure concerns a method of producing insoluble poly alpha-1,3-glucan. This method comprises: (a) contacting at least water, sucrose, and a glucosyltransferase enzyme, wherein the glucosyltransferase enzyme comprises a catalytic domain comprising the following three motifs:

-   -   (i) a motif comprising an amino acid sequence that is at least         90% identical to SEQ ID NO:78,     -   (ii) a motif comprising an amino acid sequence that is at least         90% identical to SEQ ID NO:79, and     -   (iii) a motif comprising an amino acid sequence that is at least         90% identical to SEQ ID NO:80,         wherein the glucosyltransferase enzyme does not comprise         residues 54-957 of SEQ ID NO:65, residues 55-960 of SEQ ID         NO:30, residues 55-960 of SEQ ID NO:4, residues 55-960 of SEQ ID         NO:28, or residues 55-960 of SEQ ID NO:20; whereby insoluble         poly alpha-1,3-glucan is produced having at least 95% alpha-1,3         glycosidic linkages and a weight average degree of         polymerization (DP_(w)) of at least 100; and b) optionally,         isolating the poly alpha-1,3-glucan produced in step (a).

In another embodiment, the catalytic domain comprises an amino acid sequence that is at least 90% identical to amino acid positions 54-957 of SEQ ID NO:65.

In another embodiment, the position of the amino acid sequence that is at least 90% identical to SEQ ID NO:78 aligns with amino acid positions 231-243 of SEQ ID NO:65; the position of the amino acid sequence that is at least 90% identical to SEQ ID NO:79 aligns with amino acid positions 396-425 of SEQ ID NO:65; and/or the position of the amino acid sequence that is at least 90% identical to SEQ ID NO:80 aligns with amino acid positions 549-567 of SEQ ID NO:65.

In another embodiment, motif (i) comprises SEQ ID NO:78, motif (ii) comprises SEQ ID NO:79, and motif (iii) comprises SEQ ID NO:80.

In another embodiment, the glucosyltransferase enzyme synthesizes poly alpha-1,3-glucan having 100% alpha-1,3 glycosidic linkages.

In another embodiment, the glucosyltransferase enzyme synthesizes poly alpha-1,3-glucan having a DP_(w) of at least 400.

Another embodiment of the disclosure concerns a method of identifying a glucosyltransferase enzyme. This method comprises detecting the presence of at least one motif in a glucosyltransferase catalytic domain, the at least one motif selected from the group consisting of:

-   -   (i) a motif comprising an amino acid sequence that is at least         90% identical to SEQ ID NO:78,     -   (ii) a motif comprising an amino acid sequence that is at least         90% identical to SEQ ID NO:79, and     -   (iii) a motif comprising an amino acid sequence that is at least         90% identical to SEQ ID NO:80;         thereby identifying a glucosyltransferase enzyme that produces         insoluble poly alpha-1,3-glucan having at least 95% alpha-1,3         glycosidic linkages and a weight average degree of         polymerization (DP_(w)) of at least 100.

In another embodiment, the detecting step is performed (a) in silico, (b) with a method comprising a nucleic acid hybridization step, (c) with a method comprising a protein sequencing step, and/or (d) with a method comprising a protein binding step.

In another embodiment, the detecting step comprises detecting the presence of each of motifs (i), (ii) and (iii) in the catalytic domain.

BRIEF DESCRIPTION OF THE DRAWINGS AND SEQUENCES

FIG. 1: Comparison of the main chain tertiary fold of Lactobacillus reuteri GTF (gray) and Streptococcus mutans GTF (black). The structure of the L. reuteri GTF includes a fifth domain (Domain V) that was truncated from the structure of S. mutans GTF. The active site is also indicated and is formed by a cavity in the central domains (the so-called A and B domains); this location is based on spatial similarity with similar domains in alpha amylases. The amino acid sequence of the S. mutans 3AIE GTF structure is SEQ ID NO:66, and the amino acid sequence of the L. reuteri 3KLK GTF structure is SEQ ID NO:67.

FIGS. 2A-O: Alignment of twenty-four GTF sequences with sequences of portions of GTFs from S. mutans (3AIE, SEQ ID NO:66) and L. reuteri (3KLK, SEQ ID NO:67) for which crystallographic structures are known; single-letter amino acid code is used. GTF amino acid sequences that produced glucan with 100% alpha-1,3 linkages and high molecular weight (DP_(w) of at least 400 under the tested initial sucrose concentrations, see Table 4) are designated “++”. Those GTFs producing glucan with 100% alpha-1,3 linkages and a DP_(w) of at least 100 are designated “+−”. Other GTFs producing glucan with mixed linkages are designated “−−”.

FIG. 3: The sequence of the tested GTF enzymes in the vicinity of Motifs 1a and 1b. The sequence region of Motifs 1a and 1b along with upstream and downstream flanking reference sequence motifs are shown as boxed regions. Motifs 1a and 1b are located in box labeled “Insertion 1”. The alignment in this figure represents a portion of the alignment in FIGS. 2A-O.

FIGS. 4A and 4B: Visualization of Motif 1a through comparison of a homology model of GTF 7527 (SEQ ID NO:65) based on the reference crystallographic structures of S. mutans (3AIE, SEQ ID NO:66) (FIG. 4A) and L. reuteri (3KLK, SEQ ID NO:67) (FIG. 4B). The main chain folding of the homology model in each view is shown with dark lines while the main chain folding of the reference structure is shown with lighter lines. The residues forming the catalytic sites in the reference crystallographic structures are shown as Van der Waals spheres for reference. Motif 1a (between the arrows) is presented in both homology models as an open loop (black) extending into the solvent as a consequence of there being no homologous segment to provide means to position with respect to the remainder of the GTF catalytic domain.

FIG. 5: The sequence of the tested GTF enzymes in the vicinity of Motif 2. The sequence region of Motif 2 along with upstream and downstream flanking reference sequence motifs are shown as boxed regions. Motif 2 is located in box labeled “Insertion 2”. The alignment in this figure represents a portion of the alignment in FIGS. 2A-O.

FIGS. 6A and 6B: Visualization of Motif 2 through comparison of a homology model of GTF 7527 (SEQ ID NO:65) based on the reference crystallographic structures of S. mutans (3AIE, SEQ ID NO:66) (FIG. 6A) and L. reuteri (3KLK, SEQ ID NO:67) (FIG. 6B). The main chain folding of the homology model in each view is shown with dark lines while the main chain folding of the reference structure is shown with lighter lines. The residues forming the catalytic sites in the reference crystallographic structures are shown as Van der Waals spheres for reference. Motif 2 (between the arrows) is presented in both homology models as an open loop (black) extending into the solvent as a consequence of there being no homologous segment to provide means to position with respect to the remainder of the GTF catalytic domain.

FIG. 7: The sequence of the tested GTF enzymes in the vicinity of Motifs 3a and 3b. The sequence region of Motifs 3a and 3b along with upstream and downstream flanking reference sequence motifs are shown as boxed regions. Motifs 3a and 3b are located in box labeled “Insertion 3”. The alignment in this figure represents a portion of the alignment in FIGS. 2A-O.

FIGS. 8A and 8B: Visualization of Motif 3a through comparison of a homology model of GTF 7527 (SEQ ID NO:65) based on the reference crystallographic structures of S. mutans (3AIE, SEQ ID NO:66) (FIG. 8A) and L. reuteri (3KLK, SEQ ID NO:67) (FIG. 8BA). The main chain folding of the homology model in each view is shown with dark lines while the main chain folding of the reference structure is shown with lighter lines. The residues forming the catalytic sites in the reference crystallographic structures are shown as Van der Waals spheres for reference. Motif 3a (between the arrows) is presented in both homology models as an open loop (black) extending into the solvent as a consequence of there being no homologous segment to provide means to position with respect to the remainder of the GTF catalytic domain.

TABLE 1 Summary of Nucleic Acid and Protein SEQ ID Numbers Nucleic acid Protein Description SEQ ID NO. SEQ ID NO. “0874 GTF”, Streptococcus sobrinus. DNA codon- 1 2 (1435 aa) optimized for expression in E. coli. The first 156 amino acids of the protein are deleted compared to GENBANK Identification No. 450874; a start methionine is included. “6855 GTF”, Streptococcus salivarius SK126. DNA 3 4 (1341 aa) codon-optimized for expression in E. coli. The first 178 amino acids of the protein are deleted compared to GENBANK Identification No. 228476855; a start methionine is included. “2379 GTF”, Streptococcus salivarius. DNA codon- 5 6 (1247 aa) optimized for expression in E. coli. The first 203 amino acids of the protein are deleted compared to GENBANK Identification No. 662379; a start methionine is included. “7527” or “GTFJ”, Streptococcus salivarius. DNA 7 8 (1477 aa) codon-optimized for expression in E. coli. The first 42 amino acids of the protein are deleted compared to GENBANK Identification No. 47527; a start methionine is included. “1724 GTF”, Streptococcus downei. DNA codon- 9 10 (1436 aa) optimized for expression in E. coli. The first 162 amino acids of the protein are deleted compared to GENBANK Identification No. 121724; a start methionine is included. “0544 GTF”, Streptococcus mutans. DNA codon- 11 12 (1313 aa) optimized for expression in E. coli. The first 164 amino acids of the protein are deleted compared to GENBANK Identification No. 290580544; a start methionine is included. “5926 GTF”, Streptococcus dentirousetti. DNA 13 14 (1323 aa) codon-optimized for expression in E. coli. The first 144 amino acids of the protein are deleted compared to GENBANK Identification No. 167735926; a start methionine is included. “4297 GTF”, Streptococcus oralis. DNA codon- 15 16 (1348 aa) optimized for expression in E. coli. The first 228 amino acids of the protein are deleted compared to GENBANK Identification No. 7684297; a start methionine is included. “5618 GTF”, Streptococcus sanguinis. DNA codon- 17 18 (1348 aa) optimized for expression in E. coli. The first 223 amino acids of the protein are deleted compared to GENBANK Identification No. 328945618; a start methionine is included. “2765 GTF”, unknown Streptococcus sp. C150. DNA 19 20 (1340 aa) codon-optimized for expression in E. coli. The first 193 amino acids of the protein are deleted compared to GENBANK Identification No. 322372765; a start methionine is included. “4700 GTF”, Leuconostoc mesenteroides. DNA 21 22 (1492 aa) codon-optimized for expression in E. coli. The first 36 amino acids of the protein are deleted compared to GENBANK Identification No. 21654700; a start methionine is included. “1366 GTF”, Streptococcus criceti. DNA codon- 23 24 (1323 aa) optimized for expression in E. coli. The first 139 amino acids of the protein are deleted compared to GENBANK Identification No. 146741366; a start methionine is included. “0427 GTF”, Streptococcus sobrinus. DNA codon- 25 26 (1435 aa) optimized for expression in E. coli. The first 156 amino acids of the protein are deleted compared to GENBANK Identification No. 940427; a start methionine is included. “2919 GTF”, Streptococcus salivarius PS4. DNA 27 28 (1340 aa) codon-optimized for expression in E. coli. The first 92 amino acids of the protein are deleted compared to GENBANK Identification No. 383282919; a start methionine is included. “2678 GTF”, Streptococcus salivarius K12. DNA 29 30 (1341 aa) codon-optimized for expression in E. coli. The first 188 amino acids of the protein are deleted compared to GENBANK Identification No. 400182678; a start methionine is included. “2381 GTF”, Streptococcus salivarius. DNA codon- 31 32 (1305 aa) optimized for expression in E. coli. The first 273 amino acids of the protein are deleted compared to GENBANK Identification No. 662381; a start methionine is included. “3929 GTF”, Streptococcus salivarius JIM8777. DNA 33 34 (1341 aa) codon-optimized for expression in E. coli. The first 178 amino acids of the protein are deleted compared to GENBANK Identification No. 387783929; a start methionine is included. “6907 GTF”, Streptococcus salivarius SK126. DNA 35 36 (1331 aa) codon-optimized for expression in E. coli. The first 161 amino acids of the protein are deleted compared to GENBANK Identification No. 228476907; a start methionine is included. “6661 GTF”, Streptococcus salivarius SK126. DNA 37 38 (1305 aa) codon-optimized for expression in E. coli. The first 265 amino acids of the protein are deleted compared to GENBANK Identification No. 228476661; a start methionine is included. “0339 GTF”, Streptococcus gallolyticus ATCC 43143. 39 40 (1310 aa) DNA codon-optimized for expression in E. coli. The first 213 amino acids of the protein are deleted compared to GENBANK Identification No. 334280339; a start methionine is included. “0088 GTF”, Streptococcus mutans. DNA codon- 41 42 (1267 aa) optimized for expression in E. coli. The first 189 amino acids of the protein are deleted compared to GENBANK Identification No. 3130088; a start methionine is included. “9358 GTF”, Streptococcus mutans UA159. DNA 43 44 (1287 aa) codon-optimized for expression in E. coli. The first 176 amino acids of the protein are deleted compared to GENBANK Identification No. 24379358; a start methionine is included. “8242 GTF”, Streptococcus gallolyticus ATCC BAA- 45 46 (1355 aa) 2069. DNA codon-optimized for expression in E. coli. The first 191 amino acids of the protein are deleted compared to GENBANK Identification No. 325978242; a start methionine is included. “3442 GTF”, Streptococcus sanguinis SK405. DNA 47 48 (1348 aa) codon-optimized for expression in E. coli. The first 228 amino acids of the protein are deleted compared to GENBANK Identification No. 324993442; a start methionine is included. “7528 GTF”, Streptococcus salivarius. DNA codon- 49 50 (1427 aa) optimized for expression in E. coli. The first 173 amino acids of the protein are deleted compared to GENBANK Identification No. 47528; a start methionine is included. “3279 GTF”, Streptococcus sp. C150. DNA codon- 51 52 (1393 aa) optimized for expression in E. coli. The first 178 amino acids of the protein are deleted compared to GENBANK Identification No. 322373279; a start methionine is included. “6491 GTF”, Leuconostoc citreum KM20. DNA 53 54 (1262 aa) codon-optimized for expression in E. coli. The first 244 amino acids of the protein are deleted compared to GENBANK Identification No. 170016491; a start methionine is included. “6889 GTF”, Streptococcus salivarius SK126. DNA 55 56 (1427 aa) codon-optimized for expression in E. coli. The first 173 amino acids of the protein are deleted compared to GENBANK Identification No. 228476889; a start methionine is included. “4154 GTF”, Lactobacillus reuteri. DNA codon- 57 58 (1735 aa) optimized for expression in E. coli. The first 38 amino acids of the protein are deleted compared to GENBANK Identification No. 51574154. “3298 GTF”, Streptococcus sp. C150. The first 209 59 (1242 aa) amino acids of the protein are deleted compared to GENBANK Identification No. 322373298; a start methionine is included. Wild type GTFJ, Streptococcus salivarius. GENBANK 60 (1518 aa) Identification No. 47527. Wild type GTF corresponding to 2678 GTF, 61 (1528 aa) Streptococcus salivarius K12. Wild type GTF corresponding to 6855 GTF, 62 (1518 aa) Streptococcus salivarius SK126. Wild type GTF corresponding to 2919 GTF, 63 (1431 aa) Streptococcus salivarius PS4. Wild type GTF corresponding to 2765 GTF, 64 (1532 aa) Streptococcus sp. C150. Shorter version of 7527, Streptococcus salivarius, 65 (1341 aa) (also referred to as “7527-NT” herein. The first 178 amino acids of the protein are deleted compared to GENBANK Identification No. 47527; a start methionine is included. “3AIE”, portion of a GTF from Streptococcus mutans 66 (844 aa) as annotated in the Protein Data Bank under pdb entry no. 3AIE. “3KLK”, portion of a GTF from Lactobacillus reuteri as 67 (1039 aa) annotated in the Protein Data Bank under pdb entry no. 3KLK. Catalytic active site motif FDxxRxDAxDNV 68 (12 aa) Catalytic active site motif ExWxxxDxxY 69 (10 aa) Catalytic active site motif FxRAHD 70 (6 aa) Catalytic active site motif IxNGYAF 71 (7 aa) Motif SxxRxxN upstream of Motifs 1a and 1b 72 (7 aa) Motif GGxxxLLxNDxDxSNPxVQAExLN downstream 73 (24 aa) of Motifs 1a and 1b Motif WxxxDxxY upstream of Motif 2 74 (8 aa) Motif YxFxRAHD downstream of Motif 2 75 (8 aa) Motif YxxGGQ upstream of Motifs 3a and 3b 76 (6 aa) Motif VRxG downstream of Motifs 3a and 3b 77 (4 aa) Motif 1a: D/N-K-S-I/V-L-D-E-Q-S-D-P-N-H (motif i) 78 (13 aa) Motif 2: N-K-D-G-S-K/T-A-Y-N-E-D-G-T-V/A-K-Q/K- 79 (30 aa) S-T-I-G-K-Y-N-E-K-Y-G-D-A-S (motif ii) Motif 3a: L-P-T-D-G-K-M-D-N/K-S-D-V-E-L-Y-R-T- 80 (19 aa) N/S-E (motif iii) Motif 1b: D-S/P-R-F-T-Y/F-N-A/Q/P-N-D-P 81 (11 aa) Motif 3b: I-G-N-G-E 82 (5 aa) Wild type GTF corresponding to 5926 GTF, 83 (1466 aa) Streptococcus dentirousetti. “7527-NT-dlS1a”, GTF lacking Motif 1a. DNA codon- 84 85 (1325 aa) optimized for expression in E. coli. “7527-NT-dlS2”, GTF lacking Motif 2. DNA codon- 86 87 (1311 aa) optimized for expression in E. coli. “7527-NT-dlS3a”, GTF lacking Motif 3a. DNA codon- 88 89 (1319 aa) optimized for expression in E. coli. “7527-NT-dlS1a, 2”, GTF lacking Motifs 1a and 2. 90 91 (1295 aa) DNA codon-optimized for expression in E. coli. “7527-NT-dlS1a, 3a”, GTF lacking Motifs 1a and 3a. 92 93 (1303 aa) DNA codon-optimized for expression in E. coli. “7527-NT-dlS2, 3a”, GTF lacking Motifs 2 and 3a. 94 95 (1289 aa) DNA codon-optimized for expression in E. coli. “7527-NT-dlS1a, 2, 3a”, GTF lacking Motifs 1a, 2 and 96 97 (1273 aa) 3a. DNA codon-optimized for expression in E. coli.

DETAILED DESCRIPTION

The disclosures of all patent and non-patent literature cited herein are incorporated herein by reference in their entirety.

Unless otherwise disclosed, the terms “a” and “an” as used herein are intended to encompass one or more (i.e., at least one) of a referenced feature.

Where present, all ranges are inclusive and combinable, except as otherwise noted. For example, when a range of “1 to 5” is recited, the recited range should be construed as including ranges “1 to 4”, “1 to 3”, “1-2”, “1-2 & 4-5”, “1-3 & 5”, and the like.

The terms “poly alpha-1,3-glucan”, “alpha-1,3-glucan polymer”, “glucan polymer” and the like are used interchangeably herein. Poly alpha-1,3-glucan is a polymer comprising glucose monomeric units linked together by glycosidic linkages, wherein at least about 50% of the glycosidic linkages are alpha-1,3-glycosidic linkages. Poly alpha-1,3-glucan in certain embodiments comprises at least 95% alpha-1,3-glycosidic linkages.

The terms “glycosidic linkage”, “glycosidic bond” and the like are used interchangeably herein and refer to the covalent bond that joins a carbohydrate (sugar) molecule to another group such as another carbohydrate. The term “alpha-1,3-glycosidic linkage” as used herein refers to the type of covalent bond that joins alpha-D-glucose molecules to each other through carbons 1 and 3 on adjacent alpha-D-glucose rings. The glycosidic linkages of an alpha-1,3-glucan herein can also be referred to as “glucosidic linkages”. Herein, “alpha-D-glucose” will be referred to as “glucose”.

The term “intrinsic viscosity” as used herein refers to a measure of the contribution of a glucan polymer (e.g., branched alpha-glucan) to the viscosity of a liquid (e.g., solution) comprising the glucan polymer. Intrinsic viscosity can be measured, for example using the methodology disclosed in the Examples below, or as disclosed by Weaver et al. (J. Appl. Polym. Sci. 35:1631-1637) and Chun and Park (Macromol. Chem. Phys. 195:701-711), for example.

The terms “branching index”, “branching ratio” and the like (can be denoted as g′) are used interchangeably herein, and refer to the ratio of hydrodynamic volume of a branched polymer chain with a given molar mass, to the hydrodynamic volume of a linear polymer chain with the same molar mass. Branched polymer has a smaller size in solution than its linear counterpart with the same molar mass. Thus, the branching ratio is a useful measure of the overall branching frequency in a polydispersed polymer. Branching index can be measured, for example using the methodology disclosed in the Examples below, or as disclosed by Zdunek et al. (Food Bioprocess Technol. 7:3525-3535) and Herget et al. (BMC Struct. Biol. 8:35).

The term “sucrose” herein refers to a non-reducing disaccharide composed of an alpha-D-glucose molecule and a beta-D-fructose molecule linked by an alpha-1,2-glycosidic bond. Sucrose is known commonly as table sugar.

The terms “glucosyltransferase enzyme”, “GTF enzyme”, “GTF”, “glucansucrase” and the like are used interchangeably herein. The activity of a GTF enzyme herein catalyzes the reaction of the substrate sucrose to make the products poly alpha-1,3-glucan and fructose. Other products (byproducts) of a GTF reaction can include glucose, various soluble gluco-oligosaccharides (DP2-DP7), and leucrose. Wild type forms of GTF enzymes generally contain (in the N-terminal to C-terminal direction) a signal peptide, a variable domain, a catalytic domain, and a glucan-binding domain. A GTF herein is classified under the glycoside hydrolase family 70 (GH70) according to the CAZy (Carbohydrate-Active EnZymes) database (Cantarel et al., Nucleic Acids Res. 37:D233-238, 2009).

The term “glucosyltransferase catalytic domain” herein refers to the domain of a glucosyltransferase enzyme that provides poly alpha-1,3-glucan-synthesizing activity to a glucosyltransferase enzyme. A glucosyltransferase catalytic domain preferably does not require the presence of any other domains to have this activity.

A “reaction solution” as used herein generally refers to a solution comprising sucrose, water, at least one active glucosyltransferase enzyme, and optionally other components. A reaction solution can alternatively be referred to herein as a “glucan synthesis reaction”, “glucan reaction”, “GTF reaction”, or “reaction composition”, for example. Other components that can be in a glucan synthesis reaction include fructose, glucose, leucrose, and soluble gluco-oligosaccharides (e.g., DP2-DP7). It would be understood that certain glucan products, such as poly alpha-1,3-glucan with a degree of polymerization (DP) of at least 8 or 9, are water-insoluble and thus are not dissolved in a glucan synthesis reaction, but rather may be present out of solution. It is in a reaction solution where the step of contacting water, sucrose and a glucosyltransferase enzyme is performed. The term “under suitable reaction conditions” as used herein refers to reaction conditions that support conversion of sucrose to poly alpha-1,3-glucan via glucosyltransferase enzyme activity. A reaction solution as claimed herein is not believed to be naturally occurring.

The “percent dry solids” of a reaction solution refers to the wt % of all the sugars in the glucan synthesis reaction. The percent dry solids of a reaction solution can be calculated, for example, based on the amount of sucrose used to prepare the reaction.

The “yield” of poly alpha-1,3-glucan by a reaction solution herein represents the weight of poly alpha-1,3-glucan product expressed as a percentage of the weight of sucrose substrate that is converted in the reaction. For example, if 100 g of sucrose in a reaction solution is converted to products, and 10 g of the products is poly alpha-1,3-glucan, the yield of the poly alpha-1,3-glucan would be 10%. This yield calculation can be considered as a measure of selectivity of the reaction toward poly alpha-1,3-glucan.

The term “motif” herein refers to a distinctive and recurring structural unit, such as within an amino acid sequence. By “recurring” it is meant that a motif occurs in multiple related polypeptides, for example.

The term “motif (i)” as used herein refers to an amino acid sequence comprising a sequence that is at least 90% identical to SEQ ID NO:78 (Motif 1a, Table 1).

The term “motif (ii)” as used herein refers to an amino acid sequence comprising a sequence that is at least 90% identical to SEQ ID NO:79 (Motif 2, Table 1).

The term “motif (iii)” as used herein refers to an amino acid sequence comprising a sequence that is at least 90% identical to SEQ ID NO:80 (Motif 3a, Table 1).

The terms “percent by volume”, “volume percent”, “vol %”, “v/v %” and the like are used interchangeably herein. The percent by volume of a solute in a solution can be determined using the formula: [(volume of solute)/(volume of solution)]×100%.

The terms “percent by weight”, “weight percentage (wt %)”, “weight-weight percentage (% w/w)” and the like are used interchangeably herein. Percent by weight refers to the percentage of a material on a mass basis as it is comprised in a composition, mixture, or solution.

The terms “polynucleotide”, “polynucleotide sequence”, “nucleic acid sequence”, “nucleotide sequence” and the like are used interchangeably herein. A polynucleotide may be a polymer of DNA or RNA that is single- or double-stranded, that optionally contains synthetic, non-natural or altered nucleotide bases. A polynucleotide may be comprised of one or more segments of cDNA, genomic DNA, synthetic DNA, or mixtures thereof. Nucleotides (ribonucleotides or deoxyribonucleotides) can be referred to by a single letter designation as follows: “A” for adenylate or deoxyadenylate (for RNA or DNA, respectively), “C” for cytidylate or deoxycytidylate (for RNA or DNA, respectively), “G” for guanylate or deoxyguanylate (for RNA or DNA, respectively), “U” for uridylate (for RNA), “T” for deoxythymidylate (for DNA), “R” for purines (A or G), “Y” for pyrimidines (C or T), “K” for G or T, “H” for A or C or T, “I” for inosine, “W” for A or T, and “N” for any nucleotide (e.g., N can be A, C, T, or G, if referring to a DNA sequence; N can be A, C, U, or G, if referring to an RNA sequence).

The term “gene” as used herein refers to a DNA polynucleotide sequence that expresses an RNA (RNA is transcribed from the DNA polynucleotide sequence) from a coding region, which RNA can be a messenger RNA (encoding a protein) or a non-protein-coding RNA. A gene may refer to the coding region alone, or may include regulatory sequences upstream and/or downstream to the coding region (e.g., promoters, 5′-untranslated regions, 3′-transcription terminator regions). A coding region encoding a protein can alternatively be referred to herein as an “open reading frame” (ORF). A gene that is “native” or “endogenous” refers to a gene as found in nature with its own regulatory sequences; such a gene is located in its natural location in the genome of a host cell. A “chimeric” gene refers to any gene that is not a native gene, comprising regulatory and coding sequences that are not found together in nature (i.e., the regulatory and coding regions are heterologous with each other). Accordingly, a chimeric gene may comprise regulatory sequences and coding sequences that are derived from different sources, or regulatory sequences and coding sequences derived from the same source, but arranged in a manner different than that found in nature. A “foreign” or “heterologous” gene refers to a gene that is introduced into the host organism by gene transfer. Foreign/heterologous genes can comprise native genes inserted into a non-native organism, native genes introduced into a new location within the native host, or chimeric genes. Polynucleotide sequences in certain embodiments herein are heterologous. A “transgene” is a gene that has been introduced into the genome by a gene delivery procedure (e.g., transformation). A “codon-optimized” open reading frame has its frequency of codon usage designed to mimic the frequency of preferred codon usage of the host cell.

A “non-native” amino acid sequence or polynucleotide sequence herein comprised in a cell or organism herein does not occur in a native (natural) counterpart of such cell or organism.

“Regulatory sequences” as used herein refer to nucleotide sequences located upstream of a gene's transcription start site (e.g., promoter), 5′ untranslated regions, introns, and 3′ non-coding regions, and which may influence the transcription, processing or stability, and/or translation of an RNA transcribed from the gene. Regulatory sequences herein may include promoters, enhancers, silencers, 5′ untranslated leader sequences, introns, polyadenylation recognition sequences, RNA processing sites, effector binding sites, stem-loop structures, and other elements involved in regulation of gene expression. One or more regulatory elements herein may be heterologous to a coding region herein.

A “promoter” as used herein refers to a DNA sequence capable of controlling the transcription of RNA from a gene. In general, a promoter sequence is upstream of the transcription start site of a gene. Promoters may be derived in their entirety from a native gene, or be composed of different elements derived from different promoters found in nature, or even comprise synthetic DNA segments. Promoters that cause a gene to be expressed in a cell at most times under all circumstances are commonly referred to as “constitutive promoters”. One or more promoters herein may be heterologous to a coding region herein.

A “strong promoter” as used herein refers to a promoter that can direct a relatively large number of productive initiations per unit time, and/or is a promoter driving a higher level of gene transcription than the average transcription level of the genes in a cell.

The terms “3′ non-coding sequence”, “transcription terminator”, “terminator” and the like as used herein refer to DNA sequences located downstream of a coding sequence. This includes polyadenylation recognition sequences and other sequences encoding regulatory signals capable of affecting mRNA processing or gene expression.

As used herein, a first nucleic acid sequence is “hybridizable” to a second nucleic acid sequence when a single-stranded form of the first nucleic acid sequence can anneal to the second nucleic acid sequence under suitable annealing conditions (e.g., temperature, solution ionic strength). Hybridization and washing conditions are well known and exemplified in Sambrook J, Fritsch E F and Maniatis T, Molecular Cloning: A Laboratory Manual, 2nd ed., Cold Spring Harbor Laboratory: Cold Spring Harbor, N.Y. (1989), which is incorporated herein by reference, particularly Chapter 11 and Table 11.1.

The term “DNA manipulation technique” refers to any technique in which the sequence of a DNA polynucleotide sequence is modified. Although the DNA polynucleotide sequence being modified can be used as a substrate itself for modification, it does not have to be physically in hand for certain techniques (e.g., a sequence stored in a computer can be used as the basis for the manipulation technique). A DNA manipulation technique can be used to delete and/or mutate one or more DNA sequences in a longer sequence. Examples of a DNA manipulation technique include recombinant DNA techniques (restriction and ligation, molecular cloning), polymerase chain reaction (PCR), and synthetic DNA methods (e.g., oligonucleotide synthesis and ligation). Regarding synthetic DNA techniques, a DNA manipulation technique can entail observing a DNA polynucleotide in silico, determining desired modifications (e.g., one or more deletions) of the DNA polynucleotide, and synthesizing a DNA polynucleotide that contains the desired modifications.

The term “in silico” herein means in or on an information storage and/or processing device such as a computer; done or produced using computer software or simulation, i.e., virtual reality.

The terms “cassette”, “expression cassette”, “gene cassette” and the like are used interchangeably herein. A cassette can refer to a promoter operably linked to a DNA sequence encoding a protein-coding RNA. A cassette may optionally be operably linked to a 3′ non-coding sequence. The structure of a cassette herein can optionally be represented by the simple notation system of “X::Y::Z”. Specifically, X describes a promoter, Y describes a coding sequence, and Z describes a terminator (optional); X is operably linked to Y, and Y is operably linked to Z.

The terms “upstream” and “downstream” as used herein with respect to polynucleotides refer to “5′ of” and “3′ of”, respectively.

The term “expression” as used herein refers to (i) transcription of RNA (e.g., mRNA or a non-protein-coding RNA) from a coding region, and/or (ii) translation of a polypeptide from mRNA. Expression of a coding region of a polynucleotide sequence can be up-regulated or down-regulated in certain embodiments.

The term “operably linked” as used herein refers to the association of two or more nucleic acid sequences such that the function of one is affected by the other. For example, a promoter is operably linked with a coding sequence when it is capable of affecting the expression of that coding sequence. That is, the coding sequence is under the transcriptional control of the promoter. A coding sequence can be operably linked to one (e.g., promoter) or more (e.g., promoter and terminator) regulatory sequences, for example.

The term “recombinant” when used herein to characterize a DNA sequence such as a plasmid, vector, or construct refers to an artificial combination of two otherwise separated segments of sequence, e.g., by chemical synthesis and/or by manipulation of isolated segments of nucleic acids by genetic engineering techniques. Methods for preparing recombinant constructs/vectors herein can follow standard recombinant DNA and molecular cloning techniques as described by J. Sambrook and D. Russell (Molecular Cloning: A Laboratory Manual, 3rd Edition, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y., 2001); T. J. Silhavy et al. (Experiments with Gene Fusions, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y., 1984); and F. M. Ausubel et al. (Short Protocols in Molecular Biology, 5th Ed. Current Protocols, John Wiley and Sons, Inc., NY, 2002), for example.

The term “transformation” as used herein refers to the transfer of a nucleic acid molecule into a host organism or host cell by any method. A nucleic acid molecule that has been transformed into an organism/cell may be one that replicates autonomously in the organism/cell, or that integrates into the genome of the organism/cell, or that exists transiently in the cell without replicating or integrating. Non-limiting examples of nucleic acid molecules suitable for transformation are disclosed herein, such as plasmids and linear DNA molecules. Host organisms/cells herein containing a transforming nucleic acid sequence can be referred to as “transgenic”, “recombinant”, “transformed”, “engineered”, as a “transformant”, and/or as being “modified for exogenous gene expression”, for example.

The terms “sequence identity” or “identity” as used herein with respect to polynucleotide or polypeptide sequences refer to the nucleic acid bases or amino acid residues in two sequences that are the same when aligned for maximum correspondence over a specified comparison window. Thus, “percentage of sequence identity” or “percent identity” refers to the value determined by comparing two optimally aligned sequences over a comparison window, wherein the portion of the polynucleotide or polypeptide sequence in the comparison window may comprise additions or deletions (i.e., gaps) as compared to the reference sequence (which does not comprise additions or deletions) for optimal alignment of the two sequences. The percentage is calculated by determining the number of positions at which the identical nucleic acid base or amino acid residue occurs in both sequences to yield the number of matched positions, dividing the number of matched positions by the total number of positions in the window of comparison and multiplying the results by 100 to yield the percentage of sequence identity. It would be understood that, when calculating sequence identity between a DNA sequence and an RNA sequence, T residues of the DNA sequence align with, and can be considered “identical” with, U residues of the RNA sequence. For purposes of determining “percent complementarity” of first and second polynucleotides, one can obtain this by determining (i) the percent identity between the first polynucleotide and the complement sequence of the second polynucleotide (or vice versa), for example, and/or (ii) the percentage of bases between the first and second polynucleotides that would create canonical Watson and Crick base pairs.

The Basic Local Alignment Search Tool (BLAST) algorithm, which is available online at the National Center for Biotechnology Information (NCBI) website, may be used, for example, to measure percent identity between or among two or more of the polynucleotide sequences (BLASTN algorithm) or polypeptide sequences (BLASTP algorithm) disclosed herein. Alternatively, percent identity between sequences may be performed using a Clustal algorithm (e.g., ClustalW, ClustalV, or Clustal-Omega). For multiple alignments using a Clustal method of alignment, the default values may correspond to GAP PENALTY=10 and GAP LENGTH PENALTY=10. Default parameters for pairwise alignments and calculation of percent identity of protein sequences using a Clustal method may be KTUPLE=1, GAP PENALTY=3, WINDOW=5 and DIAGONALS SAVED=5. For nucleic acids, these parameters may be KTUPLE=2, GAP PENALTY=5, WINDOW=4 and DIAGONALS SAVED=4. Alternatively still, percent identity between sequences may be performed using an EMBOSS algorithm (e.g., needle) with parameters such as GAP OPEN=10, GAP EXTEND=0.5, END GAP PENALTY=false, END GAP OPEN=10, END GAP EXTEND=0.5 using a BLOSUM matrix (e.g., BLOSUM62).

Various polypeptide amino acid sequences and polynucleotide sequences are disclosed herein as features of certain embodiments. Variants of these sequences that are at least about 70-85%, 85-90%, or 90%-95% identical to the sequences disclosed herein can be used or referenced. Alternatively, a variant amino acid sequence or polynucleotide sequence can have at least 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% identity with a sequence disclosed herein. The variant amino acid sequence or polynucleotide sequence has the same function/activity of the disclosed sequence, or at least about 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% of the function/activity of the disclosed sequence. Any polypeptide amino acid sequence disclosed herein not beginning with a methionine can typically further comprise at least a start-methionine at the N-terminus of the amino acid sequence.

All the amino acid residues at each amino acid position of the proteins disclosed herein are examples. Given that certain amino acids share similar structural and/or charge features with each other (i.e., conserved), the amino acid at each position of a protein herein can be as provided in the disclosed sequences or substituted with a conserved amino acid residue (“conservative amino acid substitution”) as follows:

-   -   1. The following small aliphatic, nonpolar or slightly polar         residues can substitute for each other: Ala (A), Ser (S), Thr         (T), Pro (P), Gly (G);     -   2. The following polar, negatively charged residues and their         amides can substitute for each other: Asp (D), Asn (N), Glu (E),         Gln (Q);     -   3. The following polar, positively charged residues can         substitute for each other: His (H), Arg (R), Lys (K);     -   4. The following aliphatic, nonpolar residues can substitute for         each other: Ala (A), Leu (L), Ile (I), Val (V), Cys (C), Met         (M); and     -   5. The following large aromatic residues can substitute for each         other: Phe (F), Tyr (Y), Trp (W).

The term “isolated” as used herein refers to a polynucleotide or polypeptide molecule that has been completely or partially purified from its native source. In some instances, the isolated polynucleotide or polypeptide molecule is part of a greater composition, buffer system or reagent mix. For example, the isolated polynucleotide or polypeptide molecule can be comprised within a cell or organism in a heterologous manner. “Isolated” herein can also characterize embodiments that are synthetic/man-made, and/or have properties that are not naturally occurring.

The term “increased” as used herein can refer to a quantity or activity that is at least about 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 50%, 100%, or 200% more than the quantity or activity for which the increased quantity or activity is being compared. The terms “increased”, “elevated”, “enhanced”, “greater than”, “improved” and the like are used interchangeably herein.

Glucosyltransferase enzymes that can synthesize high molecular weight, linear alpha-1,3-glucan polymer are sought after. Thus, some embodiments disclosed herein concern a reaction solution comprising water, sucrose, and a glucosyltransferase enzyme, wherein the glucosyltransferase enzyme comprises a catalytic domain comprising the following three motifs:

-   -   (i) a motif comprising an amino acid sequence that is at least         90% identical to SEQ ID NO:78,     -   (ii) a motif comprising an amino acid sequence that is at least         90% identical to SEQ ID NO:79, and     -   (iii) a motif comprising an amino acid sequence that is at least         90% identical to SEQ ID NO:80;         wherein the glucosyltransferase enzyme does not comprise SEQ ID         NO:4, 20, 28, 30, 65, residues 54-957 of SEQ ID NO:65, residues         55-960 of SEQ ID NO:30, residues 55-960 of SEQ ID NO:4, residues         55-960 of SEQ ID NO:28, or residues 55-960 of SEQ ID NO:20.         Significantly, the glucosyltransferase enzyme(s) in such         reaction solutions produces insoluble poly alpha-1,3-glucan         having at least 95% alpha-1,3 glycosidic linkages and a weight         average degree of polymerization (DP_(w)) of at least 100. Such         glucan, which is mostly or completely linear, is suitable for         use in spinning fibers and in other industrial applications.

The molecular weight of poly alpha-1,3-glucan produced by glucosyltransferase enzymes herein can be measured as DP_(w) (weight average degree of polymerization) or DPn (number average degree of polymerization). Alternatively, the molecular weight of poly alpha-1,3-glucan herein can be measured as number-average molecular weight (M_(n)) or as weight-average molecular weight (M_(w)). Alternatively still, molecular weight can be measured in terms of Daltons or grams/mole.

Poly alpha-1,3-glucan in certain embodiments can have a molecular weight in DP_(w) or DP_(n) of at least about 100. For example, the molecular weight can be at least about 400 DP_(w) or DP_(n). DP_(w) or DP_(n) in still another embodiment can be at least about 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, or 1000 (or any integer between 100 and 1000).

The molecular weight of poly alpha-1,3-glucan can be measured using any of several means known in the art. For example, glucan polymer molecular weight can be measured using high-pressure liquid chromatography (HPLC), size exclusion chromatography (SEC), or gel permeation chromatography (GPC).

Poly alpha-1,3-glucan in certain embodiments has at least about 95%, 96%, 97%, 98%, 99%, or 100% alpha-1,3 glycosidic linkages. In some embodiments, accordingly, poly alpha-1,3-glucan has less than about 5%, 4%, 3%, 2%, 1% or 0% of glycosidic linkages that are not alpha-1,3. It should be understood that the higher the percentage of alpha-1,3-glycosidic linkages present in poly alpha-1,3-glucan, the greater the probability that the poly alpha-1,3-glucan is linear, since there are lower occurrences of certain glycosidic linkages forming branch points in the polymer. Thus, poly alpha-1,3-glucan with 100% alpha-1,3 glycosidic linkages is completely linear. In certain embodiments, poly alpha-1,3-glucan has no branch points or less than about 5%, 4%, 3%, 2%, or 1% branch points as a percent of the glycosidic linkages in the polymer. Examples of branch points include alpha-1,6 branch points.

The glycosidic linkage profile of poly alpha-1,3-glucan herein can be determined using any method known in the art. For example, the linkage profile can be determined using methods that use nuclear magnetic resonance (NMR) spectroscopy (e.g., ¹³C NMR or ¹H NMR). These and other methods that can be used are disclosed in Food Carbohydrates: Chemistry, Physical Properties, and Applications (S. W. Cui, Ed., Chapter 3, S. W. Cui, Structural Analysis of Polysaccharides, Taylor & Francis Group LLC, Boca Raton, Fla., 2005), which is incorporated herein by reference.

Poly alpha-1,3-glucan produced by a glucosyltransferase herein is typically insoluble in most aqueous systems. In general, the solubility of a glucan polymer in an aqueous systems is related to its linkage type, molecular weight and/or degree of branching. Poly alpha-1,3-glucan is generally insoluble at a DP_(w) of 8 and above in aqueous (or mostly aqueous) liquids at 20° C. A glucosyltransferase enzyme herein can produce poly alpha-1,3-glucan as presently disclosed.

A glucosyltransferase enzyme in certain embodiments further comprises a glucosyltransferase catalytic domain comprising an amino acid sequence that is at least 90% identical to amino acid positions 54-957 of SEQ ID NO:65, and have glucosyltransferase activity. Alternatively, a glucosyltransferase catalytic domain can comprise an amino acid sequence that is, for example, at least 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 98.5%, 99%, or 99.5% (but not 100%) identical to amino acid positions 54-957 of SEQ ID NO:65, and have glucosyltransferase activity.

SEQ ID NOs:65 (GTF 7527), 30 (GTF 2678), 4 (GTF 6855), 28 (GTF 2919), and 20 (GTF 2765) each represent a glucosyltransferase that, compared to its respective wild type counterpart, lacks the signal peptide domain and all or a substantial portion of the variable domain. Thus, each of these glucosyltransferase enzymes has a catalytic domain followed by a glucan-binding domain. The approximate location of catalytic domain sequences in these enzymes is as follows: 7527 (residues 54-957 of SEQ ID NO:65), 2678 (residues 55-960 of SEQ ID NO:30), 6855 (residues 55-960 of SEQ ID NO:4), 2919 (residues 55-960 of SEQ ID NO:28), 2765 (residues 55-960 of SEQ ID NO:20). The amino acid sequences of catalytic domains of GTFs 2678, 6855, 2919 and 2765 have about 94.9%, 99.0%, 95.5% and 96.4% identity, respectively, with a catalytic domain sequence of 7527 (i.e., amino acids 54-957 of SEQ ID NO:65) (Table 4). These particular glucosyltransferase enzymes can produce poly alpha-1,3-glucan with 100% alpha-1,3 linkages and a DP_(w) of at least 400 (Table 4). Thus, a glucosyltransferase enzyme in certain embodiments can comprise, or consist of, a glucosyltransferase catalytic domain that is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 98.5%, 99%, or 99.5% (but not 100%) identical to the amino acid sequence of a catalytic domain of GTF 2678, 6855, 2919, or 2765. In some embodiments, a glucosyltransferase catalytic domain sequence does not comprise residues 54-957 of SEQ ID NO:65, residues 55-960 of SEQ ID NO:30, residues 55-960 of SEQ ID NO:4, residues 55-960 of SEQ ID NO:28, or residues 55-960 of SEQ ID NO:20.

Amino acid positions 54-957 of SEQ ID NO:65 represent, approximately, a catalytic domain sequence of the glucosyltransferase identified in GENBANK under GI number 47527 (SEQ ID NO:60). SEQ ID NO:65 generally represents the catalytic domain and glucan-binding domain of SEQ ID NO:60; the signal peptide and variable domains are missing from SEQ ID NO:65. As shown in Example 14, a catalytic domain sequence of SEQ ID NO:65 (residues 54-957) was able to catalyze the production of poly alpha-1,3-glucan. Example 14 also shows that a catalytic domain sequence of SEQ ID NO:14 (residues 57-906 of SEQ ID NO:14 [GTF 5926]) was able to catalyze production of poly alpha-1,3-glucan. The molecular weight of poly alpha-1,3-glucan produced by each of these catalytic domain sequences generally corresponded with the molecular weight of the product produced by their enzyme counterparts containing both the catalytic domain and glucan binding domain (refer to activity of SEQ ID NOs:65 and 14 in Table 4, DP_(w)150). Thus, it is believed that a catalytic domain sequence herein is an important structural component for a glucosyltransferase enzyme to be capable of producing poly alpha-1,3-glucan.

Although it is believed that a glucosyltransferase enzyme herein need only have a catalytic domain sequence, such as one comprising an amino acid sequence that is at least 90% identical to amino acid positions 54-957 of SEQ ID NO:65 (or positions 55-960 of SEQ ID NO:30, positions 55-960 of SEQ ID NO:4, positions 55-960 of SEQ ID NO:28, or positions 55-960 of SEQ ID NO:20), the glucosyltransferase enzyme can be comprised within a larger amino acid sequence. For example, the catalytic domain may be linked at its C-terminus to a glucan-binding domain, and/or linked at its N-terminus to a variable domain and/or signal peptide.

Still further examples of glucosyltransferase enzymes can be any as disclosed herein and that include 1-300 (or any integer there between [e.g., 10, 15, 20, 25, 30, 35, 40, 45, or 50]) residues on the N-terminus and/or C-terminus. Such additional residues may be from a corresponding wild type sequence from which the glucosyltransferase enzyme is derived, or may be a heterologous sequence such as an epitope tag (at either N- or C-terminus) or a heterologous signal peptide (at N-terminus), for example.

A glucosyltransferase enzyme herein typically lacks an N-terminal signal peptide. An expression system for producing a glucosyltransferase enzyme herein may employ an enzyme-encoding polynucleotide that further comprises sequence encoding an N-terminal signal peptide to direct extra-cellular secretion, if desired. The signal peptide in such embodiments is cleaved from the enzyme during the secretion process. The signal peptide may either be native or heterologous to the glucosyltransferase. An example of a signal peptide useful herein is one from a bacterial (e.g., a Bacillus species such as B. subtilis) or fungal species. An example of a bacterial signal peptide is an aprE signal peptide, such as one from Bacillus (e.g., B. subtilis, see Vogtentanz et al., Protein Expr. Purif. 55:40-52, which is incorporated herein by reference).

FIGS. 2A-O show that a catalytic domain sequence of GTF 7527 (residues 54-957 of SEQ ID NO:65) aligns with catalytic domain sequences of several other glucosyltransferase enzymes, with several regions showing complete conservation across all the sequences (residues with dark background). The dark background residues in FIGS. 2A-O visually map out the catalytic domain of each sequence, indicating their length to be about 850 to 900 amino acid residues long. Thus, the catalytic domain of the glucosyltransferase enzyme can be about 800-950 (or any integer between 800 and 950) amino acid residues long, for example.

Certain of the conserved regions in FIGS. 2A-O include catalytic active site motifs SEQ ID NOs:68, 69, 70, and 71 (refer to Example 3). Thus, a catalytic domain sequence of a glucosyltransferase enzyme in some aspects can contain one or more of SEQ ID NOs:68, 69, 70, and 71 in alignment, respectively, with SEQ ID NOs:68, 69, 70, and 71 as present in amino acids 54-957 of SEQ ID NO:65. Other conserved regions in FIGS. 2A-O include SEQ ID NOs:72, 73, 74, 75, 76 and 77 (refer to Example 4). Thus, a catalytic domain sequence of a glucosyltransferase enzyme in some aspects can contain one or more of SEQ ID NOs:72, 73, 74, 75, 76 and 77 in alignment, respectively, with SEQ ID NOs:72, 73, 74, 75, 76 and 77 as present in amino acids 54-957 of SEQ ID NO:65.

The catalytic domain of a glucosyltransferase enzyme herein can have activity as exhibited by a catalytic domain of a glucosyltransferase classified under the glycoside hydrolase family 70 (GH70). Such a GH70 glucosyltransferase may be found in the CAZy (Carbohydrate-Active EnZymes) database (Cantarel et al., Nucleic Acids Res. 37:D233-238, 2009), for example.

A glucosyltransferase enzyme herein can comprise a glucosyltransferase catalytic domain comprising the following three motifs:

-   -   (i) a motif comprising an amino acid sequence that is at least         90% identical to SEQ ID NO:78,     -   (ii) a motif comprising an amino acid sequence that is at least         90% identical to SEQ ID NO:79, and     -   (iii) a motif comprising an amino acid sequence that is at least         90% identical to SEQ ID NO:80.         Motif (i) corresponds with “Motif 1a” (FIG. 3). Motif (ii)         corresponds with “Motif 2” (FIG. 5). Motif (iii) corresponds         with “Motif 3a” (FIG. 7).

Motif (i) can be at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO:78. Motif (ii) can be at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO:79. Motif (iii) can be at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO:80. Thus, it can be seen that in certain embodiments, motif (i) can comprise SEQ ID NO:78, motif (ii) can comprise SEQ ID NO:79, and motif (iii) can comprise SEQ ID NO:80.

Regarding motif (i) in certain embodiments, the first residue of SEQ ID NO:78 (D/N-K-S-I/V-L-D-E-Q-S-D-P-N-H) can be an aspartate (D) and the fourth residue can be an isoleucine (I). Alternatively, the first residue can be an aspartate (D) and the fourth residue can be a valine (V), or the first residue can be an asparagine (N) and the fourth residue can be an isoleucine (I), or the first residue can be an asparagine (N) and the fourth residue can be a valine (V).

Regarding motif (ii) in certain embodiments, the sixth residue of SEQ ID NO:79 (N-K-D-G-S-K/T-A-Y-N-E-D-G-T-V/A-K-Q/K-S-T-I-G-K-Y-N-E-K-Y-G-D-A-S) can be a lysine (K), the fourteenth residue can be a valine (V), and the sixteenth residue can be a glutamine (Q). Alternatively, the sixth residue can be a lysine (K), the fourteenth residue can be an alanine (A), and the sixteenth residue can be a glutamine (Q); or the sixth residue can be a lysine (K), the fourteenth residue can be an valine (V), and the sixteenth residue can be a lysine (K). Additional examples include where the sixth residue can be a threonine (T).

Regarding motif (iii) in certain embodiments, the ninth residue of SEQ ID NO:80 (L-P-T-D-G-K-M-D-N/K-S-D-V-E-L-Y-R-T-N/S-E) can be an asparagine (N) and the eighteenth residue can be an asparagine (N). Alternatively, the ninth residue can be an asparagine (N) and the eighteenth residue can be a serine (S), or the ninth residue can be a lysine (K) and the eighteenth residue can be an asparagine (N), or the ninth residue can be a lysine (K) and the eighteenth residue can be a serine (S).

The relative positions of motif (i) (SEQ ID NO:78), motif (ii) (SEQ ID NO:79) and motif (iii) (SEQ ID NO:80) align with residues 231-243, 396-425 and 549-567, respectively, of the GTF 7527 sequence (SEQ ID NO:65) shown in FIGS. 2A-O. In certain embodiments herein,

-   -   (A) the position of the amino acid sequence that is at least 90%         identical to SEQ ID NO:78 in the glucosyltransferase catalytic         domain aligns with amino acid positions 231-243 of SEQ ID NO:65;     -   (B) the position of the amino acid sequence that is at least 90%         identical to SEQ ID NO:79 in the glucosyltransferase catalytic         domain aligns with amino acid positions 396-425 of SEQ ID NO:65;         and/or     -   (C) the position of the amino acid sequence that is at least 90%         identical to SEQ ID NO:80 in the glucosyltransferase catalytic         domain aligns with amino acid positions 549-567 of SEQ ID NO:65.         The term “aligns with” can be used interchangeably with         “corresponds to”, “corresponds with”, and the like. The relative         positions of motifs (i), (ii) and/or (iii) in a         glucosyltransferase catalytic domain can thus be determined with         reference to the above amino acid positions in SEQ ID NO:65. For         example, the sequence of a glucosyltransferase catalytic domain         can be aligned with SEQ ID NO:65 using any means known in the         art, such as through use of an alignment algorithm or software         as described above (e.g., BLASTP, ClustalW, ClustalV, EMBOSS).

The relative positions of motifs (i), (ii) and (iii) in a glucosyltransferase catalytic domain can be determined with reference to certain conserved sequences, namely SEQ ID NOs:72, 73, 74, 75, 76 and 77, if desired.

Motif 1a (SEQ ID NO:78) is flanked by upstream and downstream conserved sequences as shown in FIG. 3. Preceding Motif 1a is the sequence SxxRxxN (SEQ ID NO:72), and following this motif is the sequence GGxxxLLxNDxDxSNPxVQAExLN (SEQ ID NO:73). Thus, the position of motif (i) can be located between SEQ ID NOs:72 and 73. SEQ ID NO:72 can be directly adjacent (upstream) to motif (i), or 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15 (or 1-15) amino acid residues upstream motif (i). SEQ ID NO:73 can be directly adjacent (downstream) to motif (i), or 1, 2, 3, 4, or 5 (or 1-5) amino acid residues downstream motif (i).

Motif 2 (SEQ ID NO:79) is flanked by upstream and downstream conserved sequences as shown in FIG. 5. Specifically, preceding Motif 2 is the sequence WxxxDxxY (SEQ ID NO:74), and following this motif is the sequence YxFxRAHD (SEQ ID NO:75). Thus, the position of motif (ii) can be located between SEQ ID NOs:74 and 75. SEQ ID NO:74 can be directly adjacent (upstream) to motif (ii), or 1-65 (or any integer between 1 and 65) amino acid residues upstream motif (ii). SEQ ID NO:75 can be directly adjacent (downstream) to motif (ii), or 1, 2, 3, 4, or 5 (or 1-5) amino acid residues downstream motif (ii).

Motif 3a (SEQ ID NO:80) is flanked by upstream and downstream conserved sequences as shown in FIG. 7. Specifically, preceding Motif 3a is the sequence YxxGGQ (SEQ ID NO:76), and following this motif is the sequence VRxG (SEQ ID NO:77). Thus, the position of motif (iii) can be located between SEQ ID NOs:76 and 77. SEQ ID NO:76 can be directly adjacent (upstream) to motif (iii), or 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or 11 (or 1-11) amino acid residues upstream motif (iii). SEQ ID NO:77 can be directly adjacent (downstream) to motif (iii), or 1, 2, 3, 4, 5, 6, 7, 8, or 9 (or 1-9) amino acid residues downstream motif (iii).

Certain amino acid positions in the upstream/downstream conserved sequences SEQ ID NOs:72-77 can be any amino acid (indicated by an “x” in each sequence in Table 1). Examples of SEQ ID NOs:72 and 73 are as shown in any of the GTF sequences in FIGS. 2 and 3 at the amino acids of each GTF sequence aligning with positions 214-220 and 245-268, respectively, of SEQ ID NO:65 (GTF 7527). Examples of SEQ ID NOs:74 and 75 are as shown in any of the GTF sequences in FIGS. 2 and 5 at the amino acids of each GTF sequence aligning with positions 334-341 and 428-435, respectively, of SEQ ID NO:65 (GTF 7527). Examples of SEQ ID NOs:76 and 77 are as shown in any of the GTF sequences in FIGS. 2 and 7 at the amino acids of each GTF sequence aligning with positions 537-542 and 572-575, respectively, of SEQ ID NO:65 (GTF 7527).

A glucosyltransferase enzyme herein can be derived from any microbial source, such as a bacteria or fungus. Examples of bacterial glucosyltransferase enzymes are those derived from a Streptococcus species, Leuconostoc species or Lactobacillus species. Examples of Streptococcus species include S. salivarius, S. sobrinus, S. dentirousetti, S. downei, S. mutans, S. oralis, S. gallolyticus and S. sanguinis. Examples of Leuconostoc species include L. mesenteroides, L. amelibiosum, L. argentinum, L. carnosum, L. citreum, L. cremoris, L. dextranicum and L. fructosum. Examples of Lactobacillus species include L. acidophilus, L. delbrueckii, L. helveticus, L. salivarius, L. casei, L. curvatus, L. plantarum, L. sakei, L. brevis, L. buchneri, L. fermentum and L. reuteri.

A glucosyltransferase enzyme in some aspects does not comprise SEQ ID NO:4, SEQ ID NO:20, SEQ ID NO:28, SEQ ID NO:30, or SEQ ID NO:65. In certain embodiments, a glucosyltransferase enzyme herein does not comprise positions 2-1341 of SEQ ID NO:4, positions 2-1340 of SEQ ID NO:20, positions 2-1340 of SEQ ID NO:28, positions 2-1341 of SEQ ID NO:30, or positions 2-1341 of SEQ ID NO:65.

A glucosyltransferase enzyme herein can produce poly alpha-1,3-glucan as presently disclosed, such as is the above disclosure.

One or more different glucosyltransferase enzymes may be used in certain aspects. The glucosyltransferase enzyme in certain embodiments does not have, or has very little (less than 1%), dextransucrase, reuteransucrase, alternansucrase activity, or mutansucrase activity. A reaction solution herein may contain one, two, or more glucosyltransferase enzymes, for example.

A glucosyltransferase enzyme for a glucan synthesis reaction herein may be produced by any means known in the art. For example, a glucosyltransferase enzyme may be produced recombinantly in a heterologous expression system, such as a microbial heterologous expression system. Examples of heterologous expression systems include bacterial (e.g., E. coli such as TOP10 or MG1655; Bacillus sp.) and eukaryotic (e.g., yeasts such as Pichia sp. and Saccharomyces sp.) expression systems.

In certain embodiments, a heterologous gene expression system may be one that is designed for protein secretion. A glucosyltransferase enzyme typically comprises a signal peptide (signal sequence) in such embodiments. The signal peptide may be either its native signal peptide or a heterologous signal peptide.

A glucosyltransferase enzyme described herein may be used in any purification state (e.g., pure or non-pure). For example, a glucosyltransferase enzyme may be purified and/or isolated prior to its use. Examples of glucosyltransferase enzymes that are non-pure include those in the form of a cell lysate. A cell lysate or extract may be prepared from a bacteria (e.g., E. coli) used to heterologously express the enzyme. For example, the bacteria may be subjected to disruption using a French pressure cell. In alternative embodiments, bacteria may be homogenized with a homogenizer (e.g., APV, Rannie, Gaulin). A glucosyltransferase enzyme is typically soluble in these types of preparations. A bacterial cell lysate, extract, or homogenate herein may be used at about 0.15-0.3% (v/v), for example, in a reaction solution for producing poly alpha-1,3-glucan from sucrose.

The activity of a glucosyltransferase enzyme herein can be determined using any method known in the art. For example, glucosyltransferase enzyme activity can be determined by measuring the production of reducing sugars (fructose and glucose) in a reaction solution containing sucrose (50 g/L), dextran T10 (1 mg/mL) and potassium phosphate buffer (pH 6.5, 50 mM), where the solution is held at 22-25° C. for 24-30 hours. The reducing sugars can be measured, for instance, by adding 0.01 mL of the reaction solution to a mixture containing 1 N NaOH and 0.1% triphenyltetrazolium chloride and then monitoring the increase in absorbance at OD_(480nm) for five minutes.

A reaction solution herein refers to a solution comprising at least sucrose, water and an active glucosyltransferase enzyme, and optionally other components. Other components that can be in a glucan synthesis reaction include fructose, glucose, leucrose, soluble oligosaccharides (e.g., DP2-DP7), for example. It would be understood that certain glucan products, such as poly alpha-1,3-glucan with a DP of at least 8 or 9, may be water-insoluble and thus are not dissolved in a glucan synthesis reaction, but rather may be present out of solution. A reaction solution herein may be one that, in addition to producing insoluble glucan product, produces byproducts such as leucrose and/or soluble oligosaccharides.

The temperature of a reaction solution herein can be controlled, if desired. In certain embodiments, the temperature of the reaction is between about 5° C. to about 50° C. The temperature in certain other embodiments is between about 20° C. to about 40° C., or about 20° C. to about 30° C. (e.g., about 25° C.).

The initial concentration of sucrose in a reaction solution herein can be about 20 g/L to about 400 g/L, for example. Alternatively, the initial concentration of sucrose can be about 75 g/L to about 175 g/L, or from about 50 g/L to about 150 g/L. Alternatively still, the initial concentration of sucrose can be about 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, or 160 g/L (or any integer value between 40 and 160 g/L), for example. “Initial concentration of sucrose” refers to the sucrose concentration in a GTF reaction solution just after all the reaction solution components have been added (e.g., at least water, sucrose, GTF enzyme).

Sucrose used in a glucan synthesis reaction herein can be highly pure (≥99.5%) or be of any other purity or grade. For example, sucrose can have a purity of at least 99.0%, or can be reagent grade sucrose. As another example, incompletely refined sucrose can be used. Incompletely refined sucrose herein refers to sucrose that has not been processed to white refined sucrose. Thus, incompletely refined sucrose can be completely unrefined or partially refined. Examples of unrefined sucrose are “raw sucrose” (“raw sugar”) and solutions thereof. Examples of partially refined sucrose have not gone through one, two, three, or more crystallization steps. The ICUMSA (International Commission for Uniform Methods of Sugar Analysis) of incompletely refined sucrose herein can be greater than 150, for example. Sucrose herein may be derived from any renewable sugar source such as sugar cane, sugar beets, cassava, sweet sorghum, or corn. Suitable forms of sucrose useful herein are crystalline form or non-crystalline form (e.g., syrup, cane juice, beet juice), for example.

Methods of determining ICUMSA values for sucrose are well known in the art and disclosed by the International Commission for Uniform Methods of Sugar Analysis in ICUMSA Methods of Sugar Analysis: Official and Tentative Methods Recommended by the International Commission for Uniform Methods of Sugar Analysis (ICUMSA) (Ed. H. C. S. de Whalley, Elsevier Pub. Co., 1964), for example, which is incorporated herein by reference. ICUMSA can be measured, for example, by ICUMSA Method GS1/3-7 as described by R. J. McCowage, R. M. Urquhart and M. L. Burge (Determination of the Solution Colour of Raw Sugars, Brown Sugars and Coloured Syrups at pH 7.0—Official, Verlag Dr Albert Bartens, 2011 revision), which is incorporated herein by reference.

The pH of a glucan synthesis reaction in certain embodiments can be between about 4.0 to about 8.0. Alternatively, the pH can be about 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, or 8.0. The pH can be adjusted or controlled by the addition or incorporation of a suitable buffer, including but not limited to: phosphate, tris, citrate, or a combination thereof. Buffer concentration in a glucan synthesis reaction can be from 0 mM to about 100 mM, or about 10, 20, or 50 mM, for example.

Examples of other conditions and components suitable for carrying out a reaction solution herein are disclosed in U.S. Pat. No. 7,000,000, and U.S. Pat. Appl. Publ. Nos. 2013/0244288, 2013/0244287, 2013/0196384, 2013/0157316, and 2014/0087431, all of which are incorporated herein by reference.

The present disclosure also concerns a method for producing insoluble poly alpha-1,3-glucan comprising:

(a) contacting at least water, sucrose, and a glucosyltransferase enzyme, wherein the glucosyltransferase enzyme comprises a catalytic domain comprising the following three motifs:

-   -   (i) a motif comprising an amino acid sequence that is at least         90% identical to SEQ ID NO:78,     -   (ii) a motif comprising an amino acid sequence that is at least         90% identical to SEQ ID NO:79, and     -   (iii) a motif comprising an amino acid sequence that is at least         90% identical to SEQ ID NO:80,     -   and wherein the glucosyltransferase enzyme does not comprise SEQ         ID NO:4, 20, 28, 30, 65, residues 54-957 of SEQ ID NO:65,         residues 55-960 of SEQ ID NO:30, residues 55-960 of SEQ ID NO:4,         residues 55-960 of SEQ ID NO:28, or residues 55-960 of SEQ ID         NO:20;     -   whereby insoluble poly alpha-1,3-glucan is produced having at         least 95% alpha-1,3 glycosidic linkages and a weight average         degree of polymerization (DP_(w)) of at least 100; and         b) optionally, isolating the poly alpha-1,3-glucan produced in         step (a). Significantly, the poly alpha-1,3-glucan produced in         such a method is mostly or completely linear. This method can         thus optionally be characterized as a method of producing linear         (or mostly linear) poly alpha-1,3-glucan.

A glucan synthesis method as presently disclosed comprises contacting at least water, sucrose, and a glucosyltransferase enzyme as described herein. These and optionally other reagents can be added altogether or added in any order as discussed below. This step can comprise providing a reaction solution comprising water, sucrose and a glucosyltransferase enzyme. It will be understood that, as the glucosyltransferase enzyme synthesizes poly alpha-1,3-glucan, the reaction solution becomes a reaction mixture given that insoluble poly alpha-1,3-glucan falls out of solution as indicated by clouding of the reaction. The contacting step of the disclosed method can be performed in any number of ways. For example, the desired amount of sucrose can first be dissolved in water (optionally, other components may also be added at this stage of preparation, such as buffer components), followed by the addition of glucosyltransferase enzyme. The solution may be kept still, or agitated via stirring or orbital shaking, for example. Typically, a glucan synthesis reaction is cell-free.

Completion of a reaction in certain embodiments can be determined visually (no more accumulation of insoluble poly alpha-1,3-glucan) and/or by measuring the amount of sucrose left in the solution (residual sucrose), where a percent sucrose consumption of over about 90% can indicate reaction completion, for example. Typically, a reaction of the disclosed process will take about 12, 24, 36, 48, 60, 72, 84, or 96 hours to complete, depending on certain parameters such as the amount of sucrose and glucosyltransferase enzyme used in the reaction.

The percent sucrose consumption of a reaction in certain embodiments is at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% of the sucrose initially contacted with water and a glucosyltransferase enzyme. Alternatively, the percent sucrose consumption may be >90% or >95%.

The yield of poly alpha-1,3-glucan produced in some aspects of a glucan synthesis method herein can be at least about 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19% or 20%, based on the weight of sucrose converted in the reaction.

Poly alpha-1,3-glucan produced in the disclosed method may optionally be isolated. For example, insoluble poly alpha-1,3-glucan may be separated by centrifugation or filtration. In doing so, poly alpha-1,3-glucan is separated from most of the reaction solution, which may comprise water, fructose and certain byproducts (e.g., leucrose, soluble oligosaccharides DP2-DP7). This solution may also comprise residual sucrose and glucose monomer. Isolation can optionally further comprise washing the poly alpha-1,3-glucan one, two, or more times with water or other aqueous liquid, and/or drying the poly alpha-1,3-glucan.

A glucosyltransferase enzyme in certain embodiments of a glucan synthesis method herein can further comprise a glucosyltransferase catalytic domain comprising an amino acid sequence that is at least 90% identical to amino acid positions 54-957 of SEQ ID NO:65, and have glucosyltransferase activity. Alternatively, a glucosyltransferase catalytic domain can comprise an amino acid sequence that is, for example, at least 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 98.5%, 99%, or 99.5% (but not 100%) identical to amino acid positions 54-957 of SEQ ID NO:65, and have glucosyltransferase activity.

The above embodiments of poly alpha-1,3-glucan synthesis methods are examples. Any other feature disclosed herein can apply to a glucan synthesis method, accordingly. For example, any of the poly alpha-1,3-glucan product, glucosyltransferase enzyme (e.g., the catalytic domain and its motifs i, ii and iii), and reaction solution condition features disclosed herein can be applied as appropriate.

The present disclosure also concerns a method of identifying a glucosyltransferase enzyme. This method comprises detecting the presence at least one motif in a glucosyltransferase catalytic domain, the at least one motif selected from the group consisting of:

(i) a motif comprising an amino acid sequence that is at least 90% identical to SEQ ID NO:78,

(ii) a motif comprising an amino acid sequence that is at least 90% identical to SEQ ID NO:79, and

(iii) a motif comprising an amino acid sequence that is at least 90% identical to SEQ ID NO:80;

thereby identifying a glucosyltransferase enzyme that produces insoluble poly alpha-1,3-glucan having at least 95% alpha-1,3 glycosidic linkages and a weight average degree of polymerization (DP_(w)) of at least 100. Since the poly alpha-1,3-glucan produced in this a method is mostly or completely linear, this method can optionally be characterized as a method of identifying a glucosyltransferase enzyme that produces linear poly alpha-1,3-glucan.

It is contemplated that, although the above method comprises detecting any one of motifs (i), (ii), and (iii) in a glucosyltransferase catalytic domain, the method results in detecting a glucosyltransferase catalytic domain having all three of these motifs. This being said, a GTF identification method herein can optionally comprise detecting one of, two of, or all three, of motifs (i), (ii) and/or (iii) in a glucosyltransferase catalytic domain.

The detection step in a GTF identification method herein can comprise detecting an isolated amino acid sequence of a glucosyltransferase enzyme having motifs (i), (ii), or (iii). The detecting step can also be performed by detecting an isolated polynucleotide sequence encoding a glucosyltransferase enzyme having motifs (i), (ii), or (iii). The codons used to prepare the isolated polynucleotide sequence in such embodiments optionally are preferred codons for a species (e.g., E. coli or S. cerevisiae) that may be used to heterologously express the glucosyltransferase enzyme.

The presence of at least one of motifs (i), (ii), or (iii) in the catalytic domain of a glucosyltransferase enzyme can be detected following any means known in the art and/or any procedure described herein. For example, detection can be performed (a) in silico, (b) with a method comprising a nucleic acid hybridization step, (c) with a method comprising a protein sequencing step, and/or (d) with a method comprising a protein binding step.

Motifs (i), (ii) and (iii) were identified by in silico detection (see Example 4 below). Thus, the amino acid sequences of glucosyltransferase enzymes (and/or nucleotide sequences encoding such glucosyltransferase enzymes) stored in a computer or database (e.g., public databases such as GENBANK, EMBL, REFSEQ, GENEPEPT, SWISS-PROT, PIR, PDB) can be reviewed in silico to identify a glucosyltransferase enzyme comprising at least one of motifs (i), (ii) or (iii) in its catalytic domain, for example. Such review could comprise using any means known in the art such as through use of an alignment algorithm or software as described above (e.g., BLASTN, BLASTP, ClustalW, ClustalV, EMBOSS). The sequence of the glucosyltransferase catalytic domain being reviewed could be aligned with a catalytic domain sequence of SEQ ID NO:65 (GTF 7527), which comprises Motifs 1a (SEQ ID NO:78), 2 (SEQ ID NO:79) and 3a (SEQ ID NO:80), to detect the presence or absence of motifs (i), (ii), and/or (iii). Alternatively, the sequence of the glucosyltransferase catalytic domain being reviewed could be aligned with a catalytic domain sequence of SEQ ID NO:30 (GTF 2678), SEQ ID NO:4 (GTF 6855), SEQ ID NO:28 (GTF 2919), and/or SEQ ID NO:20 (GTF 2765), all of which comprise Motifs 1a (SEQ ID NO:78), 2 (SEQ ID NO:79) and 3a (SEQ ID NO:80), to identify the presence or absence of motifs (i), (ii), and/or (iii).

Another in silico means for detecting motifs (i), (ii), and/or (iii) in a glucosyltransferase catalytic domain sequence can comprise comparing the predicted three-dimensional structure (tertiary structure) of a glucosyltransferase catalytic domain sequence with a reference structure. The structures of both the catalytic domain being reviewed and the reference can be visually compared using any means known in the art such as with a computer program that provides a structure based on amino acid sequence input (e.g., software package MOE, Chemical Computing Group, Montreal, Canada). For example, if the reference structure lacks motif (i), (ii), and/or (iii), the comparison may detect the presence of motif (i), (ii), and/or (iii) by showing a domain(s) in the structure being reviewed that does not have a corresponding domain in the reference structure. Examples of this type of comparison are shown in FIGS. 4a, 4b, 6a, 6b, 8a and 8 b.

Alternatively, detecting a glucosyltransferase enzyme having motifs (i), (ii), and (iii) in its catalytic domain can be through using a method comprising a nucleic acid hybridization step. Such a method can comprise using DNA hybridization (e.g., Southern blot, dot blot), RNA hybridization (e.g., northern blot), or any other method that has a nucleic acid hybridization step (e.g., DNA sequencing, PCR, RT-PCR, all of which may comprise hybridization of an oligonucleotide), for example. As an example, an oligonucleotide that would hybridize to a nucleotide sequence encoding Motif 1a (SEQ ID NO:78), 2 (SEQ ID NO:79), or 3a (SEQ ID NO:80) could be used to detect its presence or absence in a polynucleotide sequence encoding the glucosyltransferase catalytic domain being reviewed. The conditions and parameters for carrying out hybridization methods in general are well known and disclosed, for example, in Sambrook J, Fritsch E F and Maniatis T, Molecular Cloning: A Laboratory Manual, Cold Spring Harbor Laboratory: Cold Spring Harbor, N.Y. (1989); Silhavy T J, Bennan M L and Enquist L W, Experiments with Gene Fusions, Cold Spring Harbor Laboratory: Cold Spring Harbor, N.Y. (1984); Ausubel F M et al., Current Protocols in Molecular Biology, published by Greene Publishing Assoc. and Wiley-Interscience, Hoboken, N.J. (1987); and Innis M A, Gelfand D H, Sninsky J J and White T J (Editors), PCR Protocols: A Guide to Methods and Applications, Academic Press, Inc., San Diego, Calif. (1990).

In another aspect, a glucosyltransferase enzyme that comprises motifs (i), (ii), and (iii) in its catalytic domain can be detected using a method comprising a protein sequencing step. Such a protein sequencing step can comprise one or more procedures such as N-terminal amino acid analysis, C-terminal amino acid analysis, Edman degradation, or mass spectrometry, for example.

In still another aspect, a glucosyltransferase enzyme that comprises motifs (i), (ii), and (iii) in its catalytic domain can be detected using a method comprising a protein binding step. Such a protein binding step could be performed using an antibody that specifically binds to one of these motifs, for example. Antibodies for identifying the presence or absence of motif (i) can be specific for an amino acid sequence that is at least 90% identical to SEQ ID NO:78. Antibodies for identifying the presence or absence of motif (ii) can be specific for an amino acid sequence that is at least 90% identical to SEQ ID NO:79. Antibodies for identifying the presence or absence of motif (iii) can be specific for an amino acid sequence that is at least 90% identical to SEQ ID NO:80.

Motif (i) can be at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO:78. Motif (ii) can be at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO:79. Motif (iii) can be at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO:80. Thus, it can be seen that in certain embodiments of a detection method herein, motif (i) can comprise SEQ ID NO:78, motif (ii) can comprise SEQ ID NO:79, and motif (iii) can comprise SEQ ID NO:80.

Regarding motif (i) in certain embodiments, the first residue of SEQ ID NO:78 (D/N-K-S-I/V-L-D-E-Q-S-D-P-N-H) can be an aspartate (D) and the fourth residue can be an isoleucine (I). Alternatively, the first residue can be an aspartate (D) and the fourth residue can be a valine (V), or the first residue can be an asparagine (N) and the fourth residue can be an isoleucine (I), or the first residue can be an asparagine (N) and the fourth residue can be a valine (V).

Regarding motif (ii) in certain embodiments, the sixth residue of SEQ ID NO:79 (N-K-D-G-S-K/T-A-Y-N-E-D-G-T-V/A-K-Q/K-S-T-I-G-K-Y-N-E-K-Y-G-D-A-S) can be a lysine (K), the fourteenth residue can be a valine (V), and the sixteenth residue can be a glutamine (Q). Alternatively, the sixth residue can be a lysine (K), the fourteenth residue can be an alanine (A), and the sixteenth residue can be a glutamine (Q); or the sixth residue can be a lysine (K), the fourteenth residue can be an valine (V), and the sixteenth residue can be a lysine (K). Additional examples include where the sixth residue can be a threonine (T).

Regarding motif (iii) in certain embodiments, the ninth residue of SEQ ID NO:80 (L-P-T-D-G-K-M-D-N/K-S-D-V-E-L-Y-R-T-N/S-E) can be an asparagine (N) and the eighteenth residue can be an asparagine (N). Alternatively, the ninth residue can be an asparagine (N) and the eighteenth residue can be a serine (S), or the ninth residue can be a lysine (K) and the eighteenth residue can be an asparagine (N), or the ninth residue can be a lysine (K) and the eighteenth residue can be a serine (S).

Any of the above features regarding the location of motifs (i), (ii) and (iii) in a glucosyltransferase enzyme catalytic domain sequence can be used appropriately to detect one or more of these motifs. The relative positions of motifs (i) (SEQ ID NO:78), (ii) (SEQ ID NO:79) and (iii) (SEQ ID NO:80) align with residues 231-243, 396-425 and 549-567, respectively, of the GTF 7527 sequence (SEQ ID NO:65) shown in FIGS. 2A-O. In certain embodiments herein,

-   -   (A) the position of the amino acid sequence that is at least 90%         identical to SEQ ID NO:78 in the glucosyltransferase catalytic         domain aligns with amino acid positions 231-243 of SEQ ID NO:65;     -   (B) the position of the amino acid sequence that is at least 90%         identical to SEQ ID NO:79 in the glucosyltransferase catalytic         domain aligns with amino acid positions 396-425 of SEQ ID NO:65;         and/or     -   (C) the position of the amino acid sequence that is at least 90%         identical to SEQ ID NO:80 in the glucosyltransferase catalytic         domain aligns with amino acid positions 549-567 of SEQ ID NO:65.

The relative position(s) of the amino acid sequence(s) detected in the glucosyltransferase catalytic domain can thus be determined with reference to the above amino acid positions in SEQ ID NO:65. For example, the sequence of a glucosyltransferase catalytic domain can be aligned with SEQ ID NO:65 using any means known in the art and/or as described above.

Alternatively, motif (i), (ii), and/or (iii) can be detected based on proximity to certain conserved sequences, namely SEQ ID NOs:72, 73, 74, 75, 76 and 77, as described above.

An identification method in some aspects can further comprise detecting a glucosyltransferase catalytic domain as presently disclosed. For example, a glucosyltransferase catalytic domain can be detected that comprises an amino acid sequence that is at least 90% identical to amino acid positions 54-957 of SEQ ID NO:65, positions 55-960 of SEQ ID NO:30, positions 55-960 of SEQ ID NO:4, positions 55-960 of SEQ ID NO:28, and/or positions 55-960 of SEQ ID NO:20. Alternatively, a glucosyltransferase catalytic domain can be detected that comprises an amino acid sequence that is at least 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 98.5%, 99%, or 99.5% (but not 100%) identical to any of the foregoing sequences. In some embodiments, an identification method does not detect a glucosyltransferase catalytic domain sequence comprising residues 54-957 of SEQ ID NO:65, residues 55-960 of SEQ ID NO:30, residues 55-960 of SEQ ID NO:4, residues 55-960 of SEQ ID NO:28, or residues 55-960 of SEQ ID NO:20.

Certain of the conserved regions in FIGS. 2A-O include catalytic active site motifs SEQ ID NOs:68, 69, 70, and 71 (refer to Example 3). Thus, a catalytic domain sequence of a glucosyltransferase enzyme in some aspects can be identified based on having one or more of SEQ ID NOs:68, 69, 70, and 71 in alignment, respectively, with SEQ ID NOs:68, 69, 70, and 71 as present in amino acids 54-957 of SEQ ID NO:65. Other conserved regions in FIGS. 2A-O include SEQ ID NOs:72, 73, 74, 75, 76 and 77 (refer to Example 4). Thus, a catalytic domain sequence of a glucosyltransferase enzyme in some aspects can be identified based on having one or more of SEQ ID NOs:72, 73, 74, 75, 76 and 77 in alignment, respectively, with SEQ ID NOs:72, 73, 74, 75, 76 and 77 as present in amino acids 54-957 of SEQ ID NO:65.

Although it is believed that a glucosyltransferase enzyme herein need only have a catalytic domain sequence, such as one comprising an amino acid sequence that is at least 90% identical to amino acid positions 54-957 of SEQ ID NO:65 (or positions 55-960 of SEQ ID NO:30, positions 55-960 of SEQ ID NO:4, positions 55-960 of SEQ ID NO:28, or positions 55-960 of SEQ ID NO:20), a glucosyltransferase enzyme identified in a method herein is typically comprised within a larger amino acid sequence. For example, the catalytic domain may be linked at its C-terminus to a glucan-binding domain, and/or linked at its N-terminus to a variable domain and/or signal peptide.

The catalytic domain of a glucosyltransferase enzyme identified herein can have activity as exhibited by a catalytic domain of a glucosyltransferase classified under the glycoside hydrolase family 70 (GH70). Such a GH70 glucosyltransferase may be found in the CAZy (Carbohydrate-Active EnZymes) database (Cantarel et al., Nucleic Acids Res. 37:D233-238, 2009), for example.

A glucosyltransferase enzyme identified herein can synthesize insoluble poly alpha-1,3-glucan having at least 95% alpha-1,3 glycosidic linkages and DP_(w) of at least 100. In certain embodiments, an identified GTF enzyme can synthesize poly alpha-1,3-glucan in which at least about 95%, 96%, 97%, 98%, 99%, or 100% of the constituent glycosidic linkages are alpha-1,3 linkages. In such embodiments, accordingly, the glucosyltransferase enzyme synthesizes poly alpha-1,3-glucan in which there is less than about 5%, 4%, 3%, 2%, 1%, or 0% of glycosidic linkages that are not alpha-1,3.

In another aspect, a glucosyltransferase enzyme identified herein can synthesize poly alpha-1,3-glucan having no branch points or less than about 5%, 4%, 3%, 2%, or 1% branch points as a percent of the glycosidic linkages in the polymer. Examples of branch points include alpha-1,6 branch points.

In still another aspect, a glucosyltransferase enzyme identified herein can synthesize poly alpha-1,3-glucan having a molecular weight in DP_(w) or DP_(n) of at least about 100. Alternatively, the glucosyltransferase enzyme may synthesize poly alpha-1,3-glucan having a molecular weight in DP_(n) or DP_(w) of at least about 400. Alternatively still, the glucosyltransferase enzyme may synthesize poly alpha-1,3-glucan having a molecular weight in DP_(n) or DP_(w) of at least about 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, or 1000 (or any integer between 100 and 1000).

A glucosyltransferase enzyme identified herein can be further analyzed, if desired. For example, if one or more of motifs i, ii, and/or iii is deleted and/or mutated (such that the one or more motifs are no longer at least 90% identical to SEQ ID NO:78, 79, or 80, respectively) from an identified glucosyltransferase (parent GTF), the modified glucosyltransferase (child GTF) can be expected to produce a branched alpha-glucan polymer. A branched alpha-glucan polymer produced by a child GTF herein can have an intrinsic viscosity and/or branching index that is reduced by at least 30%, for example, compared to the intrinsic viscosity and/or branching index of poly alpha-1,3-glucan synthesized by the corresponding parent GTF. The intrinsic viscosity and/or branching index of an alpha-glucan polymer can be measured by any means known in the art, or as provided in the below Examples.

A glucosyltransferase enzyme identified in a method as presently disclosed can optionally be produced. Such production can be by any means known in the art. For example, a glucosyltransferase enzyme can be produced recombinantly in a heterologous expression system, such as a microbial heterologous expression system (e.g., U.S. Pat. No. 7,000,000). Examples of heterologous expression systems include bacterial (e.g., E. coli such as TOP10, Bacillus sp.) and eukaryotic (e.g., yeasts such as Pichia sp. and Saccharomyces sp.) expression systems.

Non-limiting examples of compositions and methods disclosed herein include:

-   1. A reaction solution comprising water, sucrose, and a     glucosyltransferase enzyme, wherein the glucosyltransferase enzyme     comprises a catalytic domain comprising the following three motifs:     -   (i) a motif comprising an amino acid sequence that is at least         90% identical to SEQ ID NO:78,     -   (ii) a motif comprising an amino acid sequence that is at least         90% identical to SEQ ID NO:79, and     -   (iii) a motif comprising an amino acid sequence that is at least         90% identical to SEQ ID NO:80;     -   wherein the glucosyltransferase enzyme does not comprise SEQ ID         NO:4, 20, 28, 30, 65, or residues 54-957 of SEQ ID NO:65,         residues 55-960 of SEQ ID NO:30, residues 55-960 of SEQ ID NO:4,         residues 55-960 of SEQ ID NO:28, or residues 55-960 of SEQ ID         NO:20;     -   and wherein the glucosyltransferase enzyme produces insoluble         poly alpha-1,3-glucan having at least 95% alpha-1,3 glycosidic         linkages and a weight average degree of polymerization (DP_(w))         of at least 100. -   2 The reaction solution of embodiment 1, wherein the catalytic     domain comprises an amino acid sequence that is at least 90%     identical to amino acid positions 54-957 of SEQ ID NO:65. -   3. The reaction solution of embodiment 1 or 2, wherein:     -   (A) the position of the amino acid sequence that is at least 90%         identical to SEQ ID NO:78 aligns with amino acid positions         231-243 of SEQ ID NO:65;     -   (B) the position of the amino acid sequence that is at least 90%         identical to SEQ ID NO:79 aligns with amino acid positions         396-425 of SEQ ID NO:65; and/or     -   (C) the position of the amino acid sequence that is at least 90%         identical to SEQ ID NO:80 aligns with amino acid positions         549-567 of SEQ ID NO:65. -   4. The reaction solution of embodiment 1, 2, or 3, wherein motif (i)     comprises SEQ ID NO:78, motif (ii) comprises SEQ ID NO:79, and     motif (iii) comprises SEQ ID NO:80. -   5. The reaction solution of embodiment 1, 2, 3, or 4, wherein the     glucosyltransferase enzyme synthesizes poly alpha-1,3-glucan having     100% alpha-1,3 glycosidic linkages. -   6. The reaction solution of embodiment 1, 2, 3, 4, or 5, wherein the     glucosyltransferase enzyme synthesizes poly alpha-1,3-glucan having     a DP_(w) of at least 400. -   7. A method of producing insoluble poly alpha-1,3-glucan comprising:     -   (a) contacting at least water, sucrose, and a         glucosyltransferase enzyme, wherein the glucosyltransferase         enzyme comprises a catalytic domain comprising the following         three motifs:         -   (i) a motif comprising an amino acid sequence that is at             least 90% identical to SEQ ID NO:78,         -   (ii) a motif comprising an amino acid sequence that is at             least 90% identical to SEQ ID NO:79, and         -   (iii) a motif comprising an amino acid sequence that is at             least 90% identical to SEQ ID NO:80,         -   and wherein the glucosyltransferase enzyme does not comprise             SEQ ID NO:4, 20, 28, 30, 65, residues 54-957 of SEQ ID             NO:65, residues 55-960 of SEQ ID NO:30, residues 55-960 of             SEQ ID NO:4, residues 55-960 of SEQ ID NO:28, or residues             55-960 of SEQ ID NO:20;         -   whereby insoluble poly alpha-1,3-glucan is produced having             at least 95% alpha-1,3 glycosidic linkages and a weight             average degree of polymerization (DP_(w)) of at least 100;             and     -   b) optionally, isolating the poly alpha-1,3-glucan produced in         step (a). -   8. The method of embodiment 7, wherein the catalytic domain     comprises an amino acid sequence that is at least 90% identical to     amino acid positions 54-957 of SEQ ID NO:65. -   9. The method of embodiment 7 or 8, wherein:     -   (1) the position of the amino acid sequence that is at least 90%         identical to SEQ ID NO:78 aligns with amino acid positions         231-243 of SEQ ID NO:65;     -   (2) the position of the amino acid sequence that is at least 90%         identical to SEQ ID NO:79 aligns with amino acid positions         396-425 of SEQ ID NO:65; and/or     -   (3) the position of the amino acid sequence that is at least 90%         identical to SEQ ID NO:80 aligns with amino acid positions         549-567 of SEQ ID NO:65. -   10. The method of embodiment 7, 8, or 9, wherein motif (i) comprises     SEQ ID NO:78, motif (ii) comprises SEQ ID NO:79, and motif (iii)     comprises SEQ ID NO:80. -   11. The method of embodiment 7, 8, 9, or 10, wherein insoluble poly     alpha-1,3-glucan is produced in step (a) having 100% alpha-1,3     glycosidic linkages. -   12. The method of embodiment 7, 8, 9, 10, or 11, wherein insoluble     poly alpha-1,3-glucan is produced in step (a) having a DP_(w) of at     least 400. -   13. A method for identifying a glucosyltransferase enzyme, the     method comprising: detecting the presence of at least one motif in a     glucosyltransferase catalytic domain, the at least one motif     selected from the group consisting of:     -   (i) a motif comprising an amino acid sequence that is at least         90% identical to SEQ ID NO:78,     -   (ii) a motif comprising an amino acid sequence that is at least         90% identical to SEQ ID NO:79, and     -   (iii) a motif comprising an amino acid sequence that is at least         90% identical to SEQ ID NO:80;     -   thereby identifying a glucosyltransferase enzyme that produces         insoluble poly alpha-1,3-glucan having at least 95% alpha-1,3         glycosidic linkages and a weight average degree of         polymerization (DP_(w)) of at least 100. -   14. The method of embodiment 13, wherein the detecting step is     performed:     -   (a) in silico,     -   (b) with a method comprising a nucleic acid hybridization step,     -   (c) with a method comprising a protein sequencing step, and/or     -   (d) with a method comprising a protein binding step. -   15. The method of embodiment 13 or 14, wherein the detecting step     comprises detecting the presence of each of motifs (i), (ii)     and (iii) in the catalytic domain.

EXAMPLES

The present disclosure is further exemplified in the following Examples. It should be understood that these Examples, while indicating certain preferred aspects herein, are given by way of illustration only. From the above discussion and these Examples, one skilled in the art can ascertain the essential characteristics of the disclosed embodiments, and without departing from the spirit and scope thereof, can make various changes and modifications to adapt the disclosed embodiments to various uses and conditions.

Abbreviations

The meanings of some of the abbreviations used herein are as follows: “g” means gram(s), “h” means hour(s), “mL” means milliliter(s), “psi” means pound(s) per square inch, “wt %” means weight percentage, “μm” means micrometer(s), “° C.” means degrees Celsius, “mg” means milligram(s), “mm” means millimeter(s), “μL” means microliter(s), “mmol” means millimole(s), “min” means minute(s), “mol %” means mole percent, “M” means molar, “rpm” means revolutions per minute, “MPa” means megaPascals, “IV” means intrinsic viscosity, “g” means branching ratio.

General Methods

Preparation of Crude Extracts of Glucosyltransferase (GTF) Enzymes

GTF enzymes were prepared as follows. E. coli TOP10® cells (Invitrogen, Carlsbad, Calif.) were transformed with a pJexpress404®-based construct containing a particular GTF-encoding DNA sequence. Each sequence was codon-optimized to express the GTF enzyme in E. coli. Individual E. coli strains expressing a particular GTF enzyme were grown in LB (Luria broth) medium (Becton, Dickinson and Company, Franklin Lakes, N.J.) with ampicillin (100 μg/mL) at 37° C. with shaking to OD₆₀₀=0.4-0.5, at which time IPTG (isopropyl beta-D-1-thiogalactopyranoside, Cat. No. 16758, Sigma-Aldrich, St. Louis, Mo.) was added to a final concentration of 0.5 mM. The cultures were incubated for 2-4 hours at 37° C. following IPTG induction. Cells were harvested by centrifugation at 5,000×g for 15 minutes and resuspended (20% w/v) in 50 mM phosphate buffer pH 7.0 supplemented with dithiothreitol (DTT, 1.0 mM). Resuspended cells were passed through a French Pressure Cell (SLM Instruments, Rochester, N.Y.) twice to ensure >95% cell lysis. Lysed cells were centrifuged for 30 minutes at 12,000×g at 4° C. The resulting supernatant was analyzed by the BCA (bicinchoninic acid) protein assay (Sigma-Aldrich) and SDS-PAGE to confirm expression of the GTF enzyme, and the supernatant was stored at −20° C.

Determination of GTF Enzymatic Activity

GTF enzyme activity was confirmed by measuring the production of reducing sugars (fructose and glucose) in a GTF reaction solution. A reaction solution was prepared by adding a GTF extract (prepared as above) to a mixture containing sucrose (50 or 150 g/L), potassium phosphate buffer (pH 6.5, 50 mM), and optionally dextran (1 mg/mL, dextran T10, Cat. No. D9260, Sigma-Aldrich); the GTF extract was added to 2.5%-5% by volume. The reaction solution was then incubated at 22-25° C. for 24-30 hours, after which it was centrifuged. Supernatant (0.01 mL) was added to a mixture containing 1 N NaOH and 0.1% triphenyltetrazolium chloride (Sigma-Aldrich). The mixture was incubated for five minutes after which its OD₄₈₀ was determined using an ULTROSPEC spectrophotometer (Pharmacia LKB, New York, N.Y.) to gauge the presence of the reducing sugars fructose and glucose.

Determination of Glycosidic Linkages

Glycosidic linkages in the glucan product synthesized by a GTF enzyme were determined by ¹³C NMR (nuclear magnetic resonance). Dry glucan polymer (25-30 mg) was dissolved in 1 mL of deuterated dimethyl sulfoxide (DMSO) containing 3% by weight of LiCl with stirring at 50° C. Using a glass pipet, 0.8 mL of the solution was transferred into a 5-mm NMR tube. A quantitative ¹³C NMR spectrum was acquired using a Bruker Avance 500-MHz NMR spectrometer (Billerica, Mass.) equipped with a CPDUL cryoprobe at a spectral frequency of 125.76 MHz, using a spectral window of 26041.7 Hz. An inverse gated decoupling pulse sequence using waltz decoupling was used with an acquisition time of 0.629 second, an inter-pulse delay of 5 seconds, and 6000 pulses. The time domain data was transformed using an exponential multiplication of 2.0 Hz.

Determination of Number Average Degree of Polymerization (DP_(n))

The DP_(n) of a glucan product synthesized by a GTF enzyme was determined by size-exclusion chromatography (SEC). Dry glucan polymer was dissolved at 5 mg/mL in N,N-dimethyl-acetamide (DMAc) and 5% LiCl with overnight shaking at 100° C. The SEC system used was an Alliance™ 2695 separation module from Waters Corporation (Milford, Mass.) coupled with three on-line detectors: a differential refractometer 2410 from Waters, a multiangle light scattering photometer Heleos™ 8+ from Wyatt Technologies (Santa Barbara, Calif.), and a differential capillary viscometer ViscoStar™ from Wyatt. The columns used for SEC were four styrene-divinyl benzene columns from Shodex (Japan) and two linear KD-806M, KD-802 and KD-801 columns to improve resolution at the low molecular weight region of a polymer distribution. The mobile phase was DMAc with 0.11% LiCl. The chromatographic conditions used were 50° C. in the column and detector compartments, 40° C. in the sample and injector compartment, a flow rate of 0.5 mL/min, and an injection volume of 100 μL. The software packages used for data reduction were Empower™ version 3 from Waters (calibration with broad glucan polymer standard) and Astra® version 6 from Wyatt (triple detection method with column calibration).

Determination of Intrinsic Viscosity

Multidetector size exclusion chromatography (SEC) allowed measurement of molar mass distribution (MMD) using a combination of light scattering (LS) photometer and differential refractometer (DR). Molar mass (M) of the separated fractions across the polymer distribution was measured as a ratio of two detector responses:

M˜LS/DR, without any column calibration.

In a similar way, an in-line differential viscometer (DV) allowed measurement of intrinsic viscosity (IV) of the separated fractions:

IV˜DV/DR.

By plotting IV as a function of M in log-log scale, a so-called Mark-Houwink plot was obtained for samples tested.

Determination of Branching Ratio

Mark-Houwink (MH) plots were useful for estimating the degree of branching in polymers through measuring their size as a function of molar mass. Thus, the hydrodynamic size (H) of the macromolecule in dilute solution was determined as H=IV×M, so that using an MH plot, it could be seen how the size of the polymer chain changes with its molar mass. Branched polymer has a smaller size in solution than its linear counterpart with the same molar mass, and the position of the MH-plot indicates the degree of polymer branching.

To quantify the degree of branching, the branching ratio (or branching index) g′ was plotted as a function of molar mass. This index is defined as a ratio of hydrodynamic volume of branched polymer chain H_(br) with a given molar mass M, to the similar volume H_(lin) of the linear chain with the same molar mass; i.e., g′(M)=H_(br)/H_(lin) Since H is defined as a production of IV and M, and M is the same in both numerator and denominator, then g′ could be determined for each separated fraction with molar mass M directly from the corresponding MH plots as g′=IV_(br)/IV_(lin). These plots show how the degree of branching changes with the polymer molar mass. The weight-average branching index for each polymer (i.e., g′=IV_(br,w)/IV_(lin,w)) was a useful estimation of the overall branching frequency in the polydispersed polymer. A g′ value of 1, per this analysis, indicates that a polymer is linear (unbranched), whereas a g′ value <1 indicates that a polymer is branched.

Example 1 Production of GTF Enzymes

This Example describes the preparation of N-terminally truncated versions of glucosyltransferase (GTF) enzymes used in this study.

Nucleotide sequences encoding N-terminally truncated versions of GTF enzymes (Table 2, GTF ID) were synthesized using codons optimized for protein expression in E. coli. The nucleic acid products (Table 2, nt SEQ ID NO) encoding the GTF enzymes (Table 2, AA SEQ ID NO) were subcloned into pJexpresss404® (DNA2.0, Menlo Park, Calif.) to generate GTF expression plasmids (Table 2, plasmid ID). The GTF expression plasmids were used to transform E. coli TOP10 cells (Invitrogen, Carlsbad, Calif.) to generate GTF expression strains (Table 2, strain ID). Production of GTF enzymes by bacterial expression and determination of enzymatic activities were performed as described in General Methods.

TABLE 2 Production of GTF Enzymes AA nt SEQ SEQ ID Plasmid GTF ID GI No.^(a) ID NO NO ID Strain ID 0874 450874 1 2 pMP53 TOP10/pMP53 6855 228476855 3 4 pMP66 TOP10/pMP66 2379 662379 5 6 pMP65 TOP10/pMP65 7527 47527 7 8 pMP52 TOP10/pMP52 1724 121724 9 10 pMP55 TOP10/pMP55 0544 290580544 11 12 pMP67 TOP10/pMP67 5926 167735926 13 14 pMP56 TOP10/pMP56 4297 7684297 15 16 pMP70 TOP10/pMP70 5618 328945618 17 18 pMP72 TOP10/pMP72 2765 322372765 19 20 pMP85 TOP10/pMP85 4700 21654700 21 22 pMP83 TOP10/pMP83 1366 146741366 23 24 pMP86 TOP10/pMP86 0427 940427 25 26 pMP87 TOP10/pMP87 2919 383282919 27 28 pMP88 TOP10/pMP88 2678 400182678 29 30 pMP89 TOP10/pMP89 2381 662381 31 32 pMP96 TOP10/pMP96 3929 387783929 33 34 pMP97 TOP10/pMP97 6907 228476907 35 36 pMP57 TOP10/pMP57 6661 228476661 37 38 pMP62 TOP10/pMP62 0339 334280339 39 40 pMP73 TOP10/pMP73 0088 3130088 41 42 pMP69 TOP10/pMP69 9358 24379358 43 44 pMP71 TOP10/pMP71 8242 325978242 45 46 pMP68 TOP10/pMP68 3442 324993442 47 48 pMP75 TOP10/pMP75 7528 47528 49 50 pMP77 TOP10/pMP77 3279 322373279 51 52 pMP79 TOP10/pMP79 6491 170016491 53 54 pMP74 TOP10/pMP74 6889 228476889 55 56 pMP60 TOP10/pMP60 4154 51574154 57 58 pMP80 TOP10/pMP80 3298 322373298 59 pMP98 TOP10/pMP98 ^(a)GI number as provided for each respective sequence in GENBANK database (NCBI).

Example 2 Production of Glucan Polymer Using GTF Enzymes

This Example describes using the GTF enzymes prepared in Example 1 to synthesize glucan polymer.

Polymerization reactions were performed with each of the GTF enzymes prepared in Example 1. Reaction solutions were prepared comprising sucrose (50 g/L), potassium phosphate buffer (pH 6.5, 20 mM) and a GTF enzyme (2.5% extract by volume). After 24-30 hours at 22-25° C., insoluble glucan polymer product was harvested by centrifugation, washed three times with water, washed once with ethanol, and dried at 50° C. for 24-30 hours.

Glycosidic linkages in each insoluble glucan polymer product were determined by ¹³C NMR, and the DP_(n) for each insoluble polymer product was determined by SEC, as described in General Methods. These measurements are provided in Table 3 below.

TABLE 3 Polymer produced by GTF enzymes Glucan Polymer SEQ ID Reducing Insoluble Linkages GTF ID NO. Sugars Product % 1,3 % 1,6 DP_(n) 0874 2 yes yes 100 0 60 6855 4 yes yes 100 0 440 2379 6 yes yes 37 63 310 7527 8 yes yes 100 0 440 1724 10 yes yes 100 0 250 0544 12 yes yes 62 36 980 5926 14 yes yes 100 0 260 4297 16 yes yes 31 67 800 5618 18 yes yes 34 66 1020 2765 20 yes yes 100 0 280 4700 22 yes no 1366 24 yes no 0427 26 yes yes 100 0 120 2919 28 yes yes 100 0 250 2678 30 yes yes 100 0 390 2381 32 yes no 3929 34 yes yes 100 0 280 6907 36 yes no 6661 38 yes no 0339 40 yes no 0088 42 yes no 9358 44 yes no 8242 46 yes no 3442 48 yes no 7528 50 yes no 3279 52 yes no 6491 54 yes no 6889 56 yes no 4154 58 yes no 3298 59 yes no 50 50 none na no no

The following GTF enzymes produced glucan polymers comprising at least 50% alpha-1,3-linkages and having a DP_(n) of at least 100: 6855 (SEQ ID NO:4), 7527 (SEQ ID NO:8), 1724 (SEQ ID NO:10), 0544 (SEQ ID NO:12), 5926 (SEQ ID NO:14), 2765 (SEQ ID NO:20), 0427 (SEQ ID NO:26), 2919 (SEQ ID NO:28), 2678 (SEQ ID NO:30), and 3929 (SEQ ID NO:34) (refer to Table 3). The following GTF enzymes produced glucan polymers comprising 100% alpha-1,3-linkages, indicating linear polymers: 6855 (SEQ ID NO:4), 7527 (SEQ ID NO:8), 1724 (SEQ ID NO:10), 5926 (SEQ ID NO:14), 2765 (SEQ ID NO:20), 0427 (SEQ ID NO:26), 2919 (SEQ ID NO:28), 2678 (SEQ ID NO:30), and 3929 (SEQ ID NO:34). These results clearly indicate that not all GTF enzymes are capable of producing linear alpha-1,3-glucan polymer.

Example 3 Structure/Function Relationships Observed in GTF Sequences

This Example describes aligning the amino acid sequences of several GTF enzymes to determine whether they share any structures.

GTF enzymes were evaluated in Example 2 for their ability to produce glucan polymers with a focus on those enzymes that produce glucan with 100% alpha-1,3-linkages. The sequences of several of these enzymes were aligned with three dimensional structures that are formed by certain S. mutans and L. reuteri GTF sequences (3AIE [SEQ ID NO:66] and 3KLK [SEQ ID NO:67], respectively); the S. mutans and L. reuteri GTF sequences were aligned to superpose common tertiary structures using the software package MOE (Chemical Computing Group, Montreal, Canada). The sequences for each of the GTF enzymes used in the alignment contain the catalytic and glucan-binding domains of each enzyme, respectively (i.e., the N-terminal signal peptide and variable domains of each GTF are not included in the alignment). FIGS. 2A-O show the alignment. The sequences of the S. mutans and L. reuteri GTFs for which crystallographic structures are known were included in the alignment; S. mutans GTF is abbreviated as “3AIE” (SEQ ID NO:66) and L. reuteri GTF is abbreviated as “3KLK” (SEQ ID NO:67) in FIGS. 2A-O.

The alignment in FIGS. 2A-O indicates that all the aligned GTF sequences maintain numerous invariant regions (shown with dark background). These invariant sequences are located throughout the catalytic domain of each GTF (based on a homology model as opposed to an experimentally determined structure). The catalytic domains in the aligned GTFs are about 900-950 amino acid residues long and begin after position 1 (artificial start methionine) in each of the sequences shown in FIGS. 2A-O. The sequence following the catalytic domain in each GTF represents the glucan-binding domain. The aligned GTF sequences share as little as 40% sequence identity with the sequences of the known GTF structures (S. mutans 3AIE and L. reuteri 3KLK). But the alignment of these sequences in FIGS. 2A-O indicates a distributed pattern of conserved sequence motifs and patterns of specific residues that are conserved in all the aligned sequences (residues with dark background in FIGS. 2A-O). These conserved sequence motifs can be related to important structural features such as the catalytic site described below and can serve as reference points to identify unique or characteristic features that may be associated with specific performance benefits.

The catalytic site residues may be found in sequence motifs repeated in all the aligned sequences (FIGS. 2A-O). Specifically, with reference to the sequence from GTF 7527 (SEQ ID NO:65) in FIGS. 2A-O, Arg292 and Asp294 are found in the motif FDxxRxDAxDNV (SEQ ID NO:68) corresponding to Arg475 and Asp477 of S. mutans 3AIE GTF and Arg1023 and Asp1025 of L. reuteri 3KLK GTF; Glu332 is found in the sequence motif ExWxxxDxxY (SEQ ID NO:69) corresponding to Glu515 in S. mutans 3AIE GTF and Glu1063 in L. reuteri 3KLK GTF; His434 and Asp435 are found in the sequence motif FxRAHD (SEQ ID NO:70) corresponding to His587 and Asp588 in S. mutans 3AIE GTF and His1135 and Asp1136 in L. reuteri 3KLK GTF; and Tyr(Y)783 is found in the sequence motif IxNGYAF (SEQ ID NO:71) corresponding to the residues Tyr916 of S. mutans 3AIE GTF and Tyr1465 of L. reuteri 3KLK GTF.

Thus, the tested GTF enzymes have catalytic domains comprising several highly conserved regions.

Example 4 Sequence Motifs in GTF Enzymes that Synthesize High Molecular Weight Alpha-1,3-Glucan

The GTF enzymes whose sequences were aligned in FIGS. 2A-O were further evaluated for their ability to produce glucan polymers with a focus on those enzymes that produce glucan with 100% alpha-1,3-linkages (Table 4).

TABLE 4 Polymer Produced by Various GTF Enzymes Glucan Polymer Features Cat. % Cat. SEQ ID % Alpha-1,3 % Domain Domain GTF ID NO. Linkages^(a) DP_(w) 50^(b) DP_(w) 150^(b) Identity^(d) Region^(e) Identity^(f) 7527^(c) 65 100 910 577 100 54-957 100 2678 30 100 740 657 94.1 55-960 94.9 6855 4 100 835 570 98.9 55-960 99.0 2919 28 100 600 414 93.1 55-960 95.5 2765 20 100 670 93.6 55-960 96.4 0088 42 <30 44.7 55-900 50.4 0544 12 62 46.7 55-900 51.2 0427 26 100 260 43.1 55-900 51.8 0874 2 100 105 50 43.3 55-900 52.0 1724 10 100 535 55 42.9 55-900 51.3 5926 14 100 475 68 46.0 55-900 50.9 1366 24 <30 46.1 55-900 50.9 3298 59 <30 44.1 55-910 49.8 2379 6 37 44.5 60-915 50.7 6907 36 <30 55.6 55-885 61.8 5618 18 34 46.2 55-905 51.4 4297 16 31 46.5 55-905 51.2 3442 48 <30 45.8 55-905 51.0 9358 44 <30 49.7 55-915 53.6 6661 38 <30 45.6 55-895 50.5 0339 40 <30 53.7 55-895 57.5 8242 46 <30 54.1 55-910 59.4 7528 50 <30 48.1 55-915 54.2 3279 52 <30 41.8 55-900 48.7 ^(a)Glucan products having <30% alpha-1,3 linkages were soluble and not further analyzed for DP_(w). ^(b)DP_(w)50 and DP_(w)150 represent, respectively, the DP_(w) of glucan produced by a GTF in a reaction solution having an initial sucrose concentration of 50 g/L or 150 g/L. ^(c)SEQ ID NO: 65 is a shorter version of the 7527 GTF of SEQ ID NO: 8. ^(d)Percent identity of respective GTF with SEQ ID NO: 65 (per EMBOSS alignment). ^(e)Amino acid position of region within catalytic domain sequence having conservation (FIGS. 2A-O) with other listed GTF sequences (approximate location). ^(f)Percent identity of catalytic domain region with amino acid residues 54-957 of SEQ ID NO: 65 (per EMBOSS alignment).

Nine of the aligned GTF enzymes were found to produce glucan with 100% alpha-1,3-linkages, and five of these nine enzymes produced high molecular weight polymer (DP_(w)>400, Table 4). Specifically, the five GTF enzymes that displayed the property of producing high molecular weight glucan with 100% alpha-1,3-linkages are 7527 (SEQ ID NO:65), 2678 (SEQ ID NO:30), 6855 (SEQ ID NO:4), 2919 (SEQ ID NO:28) and 2765 (SEQ ID NO:20). The sequences for each of these GTFs are indicated with a “++” in FIGS. 2A-O.

Three sequence motifs were found in the amino acid sequences of all five GTF enzymes that produce high molecular weight glucan with 100% alpha-1,3-linkages, and appear as three different “insertions” situated around the catalytic domain of the known GTF structures. Briefly, these sequence motifs are designated as:

Motif 1a (SEQ ID NO: 78): D/N-K-S-I/V-L-D-E-Q-S-D-P-N-H Motif 2 (SEQ ID NO: 79): N-K-D-G-S-K/T-A-Y-N-E-D-G-T-V/A-K-Q/K-S-T-I-G-K-Y- N-E-K-Y-G-D-A-S Motif 3a (SEQ ID NO: 80): L-P-T-D-G-K-M-D-N/K-S-D-V-E-L-Y-R-T-N/S-E

The relative positions of motifs 1a, 2 and 3a align with residues 231-243, 396-425 and 549-567, respectively, of the 7527 GTF sequence (SEQ ID NO:65) in FIGS. 2A-O. These motifs appear to be conserved among GTF enzymes that synthesize high molecular weight alpha-1,3-glucan.

In the alignment shown in FIGS. 2A-O, motif 1a is flanked by upstream and downstream sequences as shown in FIG. 3. Specifically, preceding motif 1a is the sequence SxxRxxN (SEQ ID NO:72), and following motif 1a is the sequence GGxxxLLxNDxDxSNPxVQAExLN (SEQ ID NO:73). Both of these sequences were found in all the aligned GTF sequences and can serve as reference points for identifying motif 1a in other GTF sequences. In the alignment shown in FIGS. 2A-O, motif 2 is flanked by upstream and downstream sequences as shown in FIG. 5. Specifically, preceding motif 2 by about 50 amino acids is the sequence WxxxDxxY (SEQ ID NO:74) and following motif 2 is the sequence YxFxRAHD (SEQ ID NO:75). The downstream sequence (SEQ ID NO:75) includes two of the active site residues, His587 and Asp588 (numbered with respect to the S. mutans GTF structure, 3AIE). Both of these sequences were found in all the aligned GTF sequences and can serve as reference points for identifying motif 2 in other GTF sequences. In the alignment shown in FIGS. 2A-O, motif 3a is flanked by upstream and downstream sequences as shown in FIG. 7. Specifically, preceding motif 3a is sequence YxxGGQ (SEQ ID NO:76) and following motif 3a is the sequence VRxG (SEQ ID NO:77). Both of these sequences were found in all the aligned GTF sequences and can serve as reference points for identifying motif 2 in other GTF sequences.

Identification of motifs 1a (SEQ ID NO:78), 2 (SEQ ID NO:79) and 3a (SEQ ID NO:80) in the catalytic domains of GTF enzymes that synthesize high molecular weight glucan having 100% alpha-1,3-glycosidic linkages indicates that each of these motifs may be useful for identifying other GTFs with similar activity.

Example 5 Sequence Motifs in GTF Enzymes that Synthesize Low Molecular Weight Alpha-1,3-Glucan

Four GTF enzymes produced low molecular weight glucan having 100% alpha-1,3-linkages (Table 4). Specifically, these enzymes were 5926 (SEQ ID NO: 14), 0427 (SEQ ID NO: 26), 0874 (SEQ ID NO: 2) and 1724 (SEQ ID NO: 10). The sequences for each of these enzymes are indicated with a “+−” in FIGS. 2A-O. Two sequence motifs were found in the amino acid sequences of these GTF enzymes, and appear as two different “insertions” situated around the catalytic domain of the known GTF structures. Briefly, these sequence motifs are designated as:

Motif 1b (SEQ ID NO: 81): D-S/P-R-F-T-Y/F-N-A/Q/P-N-D-P Motif 3b (SEQ ID NO: 82): I-G-N-G-E

The relative positions of motifs 1b and 3b align with residues 231-243 and 549-553, respectively, of the 7527 GTF sequence (SEQ ID NO:65) in FIGS. 2A-O. Identification of motifs 1b (SEQ ID NO:81) and 3b (SEQ ID NO:82) in the catalytic domains of GTF enzymes that synthesize low molecular weight glucan having 100% alpha-1,3-glycosidic linkages indicates that each of these unique motifs may be useful for identifying other GTFs with similarly activity.

Example 6 Production of GTF Enzyme Lacking Sequence Motif 1a

A nucleotide sequence encoding a polypeptide similar to the 7527 GTF of SEQ ID NO:65, but with a deletion of Motif 1a (Example 4), was synthesized using codons optimized for expression in E. coli (DNA 2.0, Menlo Park Calif.). The nucleic acid product (SEQ ID NO:84), encoding GTF protein 7527-NT-dIS1a (SEQ ID NO:85), was subcloned into pJexpress404® (DNA 2.0, Menlo Park Calif.) to generate the plasmid identified as pMP101. Plasmid pMP101 was used to transform E. coli TOP10 cells to generate the strain identified as TOP10/pMP101. It is noted that a GTF catalytic domain sequence is located at amino acid positions 54-941 (approximate) of SEQ ID NO:85.

Production of 7527-NT-dIS1a enzyme (SEQ ID NO:85) with E. coli and production of glucan polymer using this enzyme were performed as described above (General Methods). The glucan product is insoluble, and likely comprises only alpha-glycosidic linkages. The intrinsic viscosity and branching of the glucan product (analyzed as described in General Methods) are listed in Table 5 below.

Example 7 Production of GTF Enzyme Lacking Sequence Motif 2

A nucleotide sequence encoding a polypeptide similar to the 7527 GTF of SEQ ID NO:65, but with a deletion of Motif 2 (Example 4), was synthesized using codons optimized for expression in E. coli (DNA 2.0, Menlo Park Calif.). The nucleic acid product (SEQ ID NO:86), encoding GTF protein 7527-NT-dIS2 (SEQ ID NO:87), was subcloned into pJexpress404® to generate the plasmid identified as pMP102. Plasmid pMP102 was used to transform E. coli TOP10 cells to generate the strain identified as TOP10/pMP102. It is noted that a GTF catalytic domain sequence is located at amino acid positions 54-927 (approximate) of SEQ ID NO:87.

Production of 7527-NT-dIS2 (SEQ ID NO:87) with E. coli and production of glucan polymer using this enzyme were performed as described above (General Methods). The glucan product is insoluble, and likely comprises only alpha-glycosidic linkages. The intrinsic viscosity and branching of the glucan product (analyzed as described in General Methods) are listed in Table 5 below.

Example 8 Production of GTF Enzyme Lacking Sequence Motif 3a

A nucleotide sequence encoding a polypeptide similar to the 7527 GTF of SEQ ID NO:65, but with a deletion of Motif 3a (Example 4), was synthesized using codons optimized for expression in E. coli (DNA 2.0, Menlo Park Calif.). The nucleic acid product (SEQ ID NO:88), encoding GTF protein 7527-NT-dIS3a (SEQ ID NO:89), was subcloned into pJexpress404® to generate the plasmid identified as pMP103. Plasmid pMP103 was used to transform E. coli TOP10 cells to generate the strain identified as TOP10/pMP103. It is noted that a GTF catalytic domain sequence is located at amino acid positions 54-935 (approximate) of SEQ ID NO:89.

Production of 7527-NT-dIS3a (SEQ ID NO:89) with E. coli and production of glucan polymer using this enzyme were performed as described above (General Methods). The glucan product is insoluble, and likely comprises only alpha-glycosidic linkages. The intrinsic viscosity and branching of the glucan product (analyzed as described in General Methods) are listed in Table 5 below.

Example 9 Production of GTF Enzyme Lacking Sequence Motifs 1a and 2

A nucleotide sequence encoding a polypeptide similar to the 7527 GTF of SEQ ID NO:65, but with deletion of Motifs 1a and 2 (Example 4), was synthesized using codons optimized for expression in E. coli (DNA 2.0, Menlo Park Calif.). The nucleic acid product (SEQ ID NO:90), encoding GTF protein 7527-NT-dIS1a,2 (SEQ ID NO:91), was subcloned into pJexpress404® to generate the plasmid identified as pMP104. Plasmid pMP104 was used to transform E. coli TOP10 cells to generate the strain identified as TOP10/pMP104. It is noted that a GTF catalytic domain sequence is located at amino acid positions 54-911 (approximate) of SEQ ID NO:91.

Production of 7527-NT-dIS1a,2 (SEQ ID NO:91) with E. coli and production of glucan polymer using this enzyme were performed as described above (General Methods). The glucan product is insoluble, and likely comprises only alpha-glycosidic linkages. The intrinsic viscosity and branching of the glucan product (analyzed as described in General Methods) are listed in Table 5 below.

Example 10 Production of GTF Enzyme Lacking Sequence Motifs 1a and 3a

A nucleotide sequence encoding a polypeptide similar to the 7527 GTF of SEQ ID NO:65, but with deletion of Motifs 1a and 3a (Example 4), was synthesized using codons optimized for expression in E. coli (DNA 2.0, Menlo Park Calif.). The nucleic acid product (SEQ ID NO:92), encoding GTF protein 7527-NT-dIS1a,3a (SEQ ID NO:93), was subcloned into pJexpress404® to generate the plasmid identified as pMP105. Plasmid pMP105 was used to transform E. coli TOP10 cells to generate the strain identified as TOP10/pMP105. It is noted that a GTF catalytic domain sequence is located at amino acid positions 54-919 (approximate) of SEQ ID NO:93.

Production of 7527-NT-dIS1a,3a (SEQ ID NO:93) with E. coli and production of glucan polymer using this enzyme were performed as described above (General Methods). The glucan product is insoluble, and likely comprises only alpha-glycosidic linkages. The intrinsic viscosity and branching of the glucan product (analyzed as described in General Methods) are listed in Table 5 below.

Example 11 Production of GTF Enzyme Lacking Sequence Motifs 2 and 3a

A nucleotide sequence encoding a polypeptide similar to the 7527 GTF of SEQ ID NO:65, but with deletion of Motifs 2 and 3a (Example 4), was synthesized using codons optimized for expression in E. coli (DNA 2.0, Menlo Park Calif.). The nucleic acid product (SEQ ID NO:94), encoding GTF protein 7527-NT-dIS2,3a (SEQ ID NO:95), was subcloned into pJexpress404® to generate the plasmid identified as pMP106. Plasmid pMP106 was used to transform E. coli TOP10 cells to generate the strain identified as TOP10/pMP106. It is noted that a GTF catalytic domain sequence is located at amino acid positions 54-905 (approximate) of SEQ ID NO:95.

Production of 7527-NT-dIS2,3a (SEQ ID NO:95) with E. coli and production of glucan polymer using this enzyme were performed as described above (General Methods). The glucan product is insoluble, and likely comprises only alpha-glycosidic linkages. The intrinsic viscosity and branching of the glucan product (analyzed as described in General Methods) are listed in Table 5 below.

Example 12 Production of GTF Enzyme Lacking Sequence Motifs 1a, 2 and 3a

A nucleotide sequence encoding a polypeptide similar to the 7527 GTF of SEQ ID NO:65, but with deletion of Motifs 1a, 2 and 3a (Example 4), was synthesized using codons optimized for expression in E. coli (DNA 2.0, Menlo Park Calif.). The nucleic acid product (SEQ ID NO:96), encoding GTF protein 7527-NT-dIS1a,2,3a (SEQ ID NO:97), was subcloned into pJexpress404® to generate the plasmid identified as pMP107. Plasmid pMP107 was used to transform E. coli TOP10 cells to generate the strain identified as TOP10/pMP107. It is noted that a GTF catalytic domain sequence is located at amino acid positions 54-889 (approximate) of SEQ ID NO:97.

Production of 7527-NT-dIS1a,2,3a (SEQ ID NO:97) with E. coli and production of glucan polymer using this enzyme were performed as described above (General Methods). The glucan product is insoluble, and likely comprises only alpha-glycosidic linkages. The intrinsic viscosity and branching of the glucan product (analyzed as described in General Methods) are listed in Table 5 below.

Example 13 Analysis of Intrinsic Viscosity and Branching of Glucan Products Synthesized by GTF Enzymes

This Example describes measuring the intrinsic viscosity (IV) and branching (g′) of glucan polymer synthesized by each of the deletion-containing GTF enzymes prepared in Examples 6-12. These measurements were compared to those obtained with glucan polymer produced by the 7527 GTF of SEQ ID NO:65, which does not have any internal deletions of Motifs 1a, 2 and/or 3a.

It is noted that the glucan polymer synthesized by 7527 GTF, poly alpha-1,3-glucan, has 100% alpha-1,3 linkages and is thus linear (see Table 4, for example).

The intrinsic viscosity and branching of glucan polymer samples produced by deletion-containing versions of 7527 GTF were analyzed as described in the General Methods, and are shown in Table 5 below. Non-deleted 7527 GTF is listed as “7527-NT” in Table 5. Glucan polymer produced by non-deleted 7527 GTF (control), which is listed as “7527-NT” in Table 5, was also analyzed.

TABLE 5 Intrinsic Viscosity (IV) and Branching Index (g′) of Glucan Polymer Produced by Various GTF Enzymes Glucan Product SEQ Missing Measurement Enzyme ID ID NO Motif(s) IV g′ 7527-NT 65 N/A 206 1.000 7527-NT-dlS1a 85 1a 94 0.410 7527-NT-dlS2 87 2 33 0.231 7527-NT-dlS3a 89 3a 28 0.268 7527-NT-dlS1a, 2 91 1a and 2 21 0.261 7527-NT-dlS1a, 3a 93 1a and 3a 18 0.215 7527-NT-dlS2, 3a 95 2 and 3a 19 0.256 7527-NT-dlS1a, 2, 3a 97 1a, 2 and 3a 22 0.242

As shown in Table 5, glucan produced by each GTF enzyme missing at least one of Motifs 1a (motif i), 2 (motif ii), or 3a (motif iii) had decreased intrinsic viscosity (IV) and branching index (g′), as compared to glucan produced by the corresponding control GTF (7527-NT) having each of these motifs. Since reductions in either IV and/or g′ indicate increased polymer branching, these results demonstrate that each of Motifs 1a, 2 and 3a may be essential for certain GTF enzymes—ones that naturally contain each of these motifs—to produce linear alpha-1,3-glucan polymer.

This observation was not expected, given that some GTF enzymes that produce linear product do not contain any of Motifs 1a, 2, or 3a. For example, each of GTFs 5926, 0427, 0874, and 1724 produce poly alpha-1,3-glucan with 100% alpha-1,3 linkages (which is linear) (Table 4), despite not having any of these motifs. Indeed, since there appeared to be a correlation between the presence of Motifs 1a, 2 and 3a with increased glucan product molecular weight (see Example 4), it might have been more reasonable to have expected that Motif 1a, 2, and/or 3a removal would reduce glucan product molecular weight (instead of having an effect on branching).

Thus, GTF amino acid Motifs 1a, 2 and 3a play a role in production of linear poly alpha-1,3-glucan by those GTF enzymes that contain these motifs

Example 14 GTF Catalytic Domain Activity

This Example describes testing catalytic domain sequences of certain GTFs for the ability to produce insoluble poly alpha-1,3-glucan. Specifically, catalytic domain sequences of GTFs 7527 (SEQ ID NO:65) and 5926 (SEQ ID NO:14) were tested for activity.

A GTF catalytic domain sequence having amino acid residues 54-957 of SEQ ID NO:65 was prepared using the heterologous expression techniques described above. Briefly, a DNA sequence (codon-optimized for expression in E. coli) encoding a methionine at the first amino acid position followed by amino acid residues 54-957 of SEQ ID NO:65 was prepared and used to express this catalytic domain sequence. This protein, compared to the amino acid sequence identified in GENBANK under GI number 47527 (SEQ ID NO:60), is truncated by 230 amino acids at the N-terminus and 384 amino acids at the C-terminus.

A GTF catalytic domain sequence having amino acid residues 57-906 of SEQ ID NO:14 was prepared using the heterologous expression techniques described above. Briefly, a DNA sequence (codon-optimized for expression in E. coli) encoding a methionine at the first amino acid position followed by amino acid residues 57-906 of SEQ ID NO:14 was prepared and used to express this catalytic domain sequence. This protein, compared to the amino acid sequence identified in GENBANK under GI number 167735926 (SEQ ID NO:83), is truncated by 199 amino acids at the N-terminus and 417 amino acids at the C-terminus.

The above procedures were followed to prepare reaction solutions containing either of these GTF catalytic domain sequences. The reactions were performed at 25° C. and the alpha-1,3-glucan produced in each reaction was analyzed for DP_(w). The results are provided in Table 6.

TABLE 6 Alpha-1,3-Glucan Polymer Produced by Gtf Enzyme Catalytic Domains Catalytic Initial Domain sucrose % Sucrose Sequence DP_(w) (g/L) consumption 5926 108 150 100 7527 495 142 94

As shown in Table 6, catalytic domain sequences of GTF 7527 (residues 54-957 of SEQ ID NO:65) and GTF 5926 (residues 57-906 of SEQ ID NO:14) were able to catalyze production of poly alpha-1,3-glucan. The molecular weight of the poly alpha-1,3-glucan produced by each of these catalytic domain sequences generally corresponded with the molecular weight of the product produced by their counterparts containing both the catalytic domain and glucan binding domain (refer to activity of SEQ ID NOs:65 and 14 in Table 4, DP_(w)150).

Thus, the catalytic domain of a glucosyltransferase enzyme can be used to produce insoluble poly alpha-1,3-glucan in a reaction solution. 

What is claimed is:
 1. A method for identifying a glucosyltransferase enzyme, wherein said identifying consists of: detecting the presence of at least one motif in a glucosyltransferase catalytic domain, wherein said at least one motif is selected from the group consisting of: a motif comprising an amino acid sequence that is at least 90% identical to SEQ ID NO:78, (ii) a motif comprising an amino acid sequence that is at least 90% identical to SEQ ID NO:79, and (iii) a motif comprising an amino acid sequence that is at least 90% identical to SEQ ID NO:80; thereby identifying a glucosyltransferase enzyme that produces insoluble poly alpha-1,3-glucan having at least 95% alpha-1,3 glycosidic linkages and a weight average degree of polymerization (DP_(w)) of at least
 100. 2. The method of claim 1, wherein the detecting step is performed: (a) in silico, (b) with a method comprising a nucleic acid hybridization step, (c) with a method comprising a protein sequencing step, and/or (d) with a method comprising a protein binding step.
 3. The method of claim 1, wherein said identifying consists of detecting the presence of each of motifs (i), (ii) and (iii) in said catalytic domain.
 4. The method of claim 1, further comprising, after said identifying, producing the glucosyltransferase enzyme.
 5. The method of claim 4, wherein the glucosyltransferase enzyme is produced by a method comprising recombinant expression of the glucosyltransferase enzyme.
 6. The method of claim 5, wherein said recombinant expression comprises microbial expression of the glucosyltransferase enzyme.
 7. The method of claim 4, further comprising: contacting the glucosyltransferase enzyme with at least water and sucrose, thereby producing said insoluble poly alpha-1,3-glucan.
 8. The method of claim 1, wherein the catalytic domain comprises an amino acid sequence that is at least 90% identical to amino acid positions 54-957 of SEQ ID NO:65.
 9. The method of claim 8, wherein the catalytic domain comprises an amino acid sequence that is at least 95% identical to amino acid positions 54-957 of SEQ ID NO:65.
 10. The method of claim 8, wherein (A) the position of the amino acid sequence that is at least 90% identical to SEQ ID NO:78 aligns with amino acid positions 231-243 of SEQ ID NO:65; (B) the position of the amino acid sequence that is at least 90% identical to SEQ ID NO:79 aligns with amino acid positions 396-425 of SEQ ID NO:65; and/or (C) the position of the amino acid sequence that is at least 90% identical to SEQ ID NO:80 aligns with amino acid positions 549-567 of SEQ ID NO:65.
 11. The method of claim 1, wherein the glucosyltransferase enzyme produces poly alpha-1,3-glucan having at least 99% alpha-1,3 glycosidic linkages.
 12. The method of claim 1, wherein the glucosyltransferase enzyme produces poly alpha-1,3-glucan having a DP_(w) of at least
 400. 13. The method of claim 1, wherein the glucosyltransferase enzyme produces poly alpha-1,3-glucan having 100% alpha-1,3 glycosidic linkages.
 14. The method of claim 7, wherein said insoluble poly alpha-1,3-glucan has at least 99% alpha-1,3 glycosidic linkages.
 15. The method of claim 7, wherein said insoluble poly alpha-1,3-glucan has 100% alpha-1,3 glycosidic linkages. 